tests/vm_qrexec_gui: do not swallow stderr on failure

QubesVM.run_for_stdio() by default captures stderr. In case of call fail
(non-zero return code), captured stderr is included in the exception
object, but isn't printed by default CalledProcessError message.
Make it visible by:
 - handling CalledProcessError and including in the test failure message
   (when exception is captured already)
 - not capturing stderr (if no exception handling is present in the
   test)

(cherry picked from commit 5423ead)

qubes/tests/integ/vm_qrexec_gui.py

@@ -238,6 +238,9 @@ def test_052_qrexec_vm_service_eof(self):
                             /bin/sh -c 'echo test; exec >&-; cat >&$SAVED_FD_1'
                     '''.format(self.testvm2.name)),
                     timeout=10))
+            except subprocess.CalledProcessError as e:
+                self.fail('{} exited with non-zero code {}; stderr: {}'.format(
+                    e.cmd, e.returncode, e.stderr))
             except asyncio.TimeoutError:
                 self.fail("Timeout, probably EOF wasn't transferred")
 
@@ -262,6 +265,9 @@ def test_053_qrexec_vm_service_eof_reverse(self):
                             /bin/sh -c 'cat >&$SAVED_FD_1'
                         '''.format(self.testvm2.name)),
                     timeout=10))
+            except subprocess.CalledProcessError as e:
+                self.fail('{} exited with non-zero code {}; stderr: {}'.format(
+                    e.cmd, e.returncode, e.stderr))
             except asyncio.TimeoutError:
                 self.fail("Timeout, probably EOF wasn't transferred")
 
@@ -295,6 +301,9 @@ def test_055_qrexec_dom0_service_abort(self):
                             e=$(cat /tmp/exit-code);
                             test $e -eq 141 -o $e -eq 1'''),
                     timeout=10))
+            except subprocess.CalledProcessError as e:
+                self.fail('{} exited with non-zero code {}; stderr: {}'.format(
+                    e.cmd, e.returncode, e.stderr))
             except asyncio.TimeoutError:
                 self.fail("Timeout, probably stdout wasn't closed")
 
@@ -316,15 +325,17 @@ def test_065_qrexec_exit_code_vm(self):
             (stdout, stderr) = self.loop.run_until_complete(
                 self.testvm1.run_for_stdio('''\
                     /usr/lib/qubes/qrexec-client-vm {} test.Retcode;
-                        echo $?'''.format(self.testvm2.name)))
+                        echo $?'''.format(self.testvm2.name),
+                        stderr=None))
             self.assertEqual(stdout, b'0\n')
 
             self.create_remote_file(self.testvm2, '/etc/qubes-rpc/test.Retcode',
                 'exit 3')
             (stdout, stderr) = self.loop.run_until_complete(
                 self.testvm1.run_for_stdio('''\
                     /usr/lib/qubes/qrexec-client-vm {} test.Retcode;
-                        echo $?'''.format(self.testvm2.name)))
+                        echo $?'''.format(self.testvm2.name),
+                        stderr=None))
             self.assertEqual(stdout, b'3\n')
 
     def test_070_qrexec_vm_simultaneous_write(self):
@@ -363,8 +374,9 @@ def test_070_qrexec_vm_simultaneous_write(self):
                             dd of=/dev/null bs=993 count=10000 iflag=fullblock;
                             wait'
                         '''.format(self.testvm2.name)), timeout=10))
-            except subprocess.CalledProcessError:
-                self.fail('Service call failed')
+            except subprocess.CalledProcessError as e:
+                self.fail('{} exited with non-zero code {}; stderr: {}'.format(
+                    e.cmd, e.returncode, e.stderr))
             except asyncio.TimeoutError:
                 self.fail('Timeout, probably deadlock')
 
@@ -483,7 +495,8 @@ def test_080_qrexec_service_argument_allow_default(self):
         with self.qrexec_policy('test.Argument', self.testvm1, self.testvm2):
             stdout, stderr = self.loop.run_until_complete(
                 self.testvm1.run_for_stdio('/usr/lib/qubes/qrexec-client-vm '
-                    '{} test.Argument+argument'.format(self.testvm2.name)))
+                    '{} test.Argument+argument'.format(self.testvm2.name),
+                    stderr=None))
             self.assertEqual(stdout, b'argument')
 
     def test_081_qrexec_service_argument_allow_specific(self):
@@ -502,7 +515,8 @@ def test_081_qrexec_service_argument_allow_specific(self):
                 stdout, stderr = self.loop.run_until_complete(
                     self.testvm1.run_for_stdio(
                         '/usr/lib/qubes/qrexec-client-vm '
-                        '{} test.Argument+argument'.format(self.testvm2.name)))
+                        '{} test.Argument+argument'.format(self.testvm2.name),
+                        stderr=None))
         self.assertEqual(stdout, b'argument')
 
     def test_082_qrexec_service_argument_deny_specific(self):
@@ -521,7 +535,8 @@ def test_082_qrexec_service_argument_deny_specific(self):
                     self.loop.run_until_complete(
                         self.testvm1.run_for_stdio(
                             '/usr/lib/qubes/qrexec-client-vm {} '
-                            'test.Argument+argument'.format(self.testvm2.name)))
+                            'test.Argument+argument'.format(self.testvm2.name),
+                            stderr=None))
 
     def test_083_qrexec_service_argument_specific_implementation(self):
         """Qrexec service call with argument - argument specific
@@ -540,7 +555,8 @@ def test_083_qrexec_service_argument_specific_implementation(self):
         with self.qrexec_policy('test.Argument', self.testvm1, self.testvm2):
             stdout, stderr = self.loop.run_until_complete(
                 self.testvm1.run_for_stdio('/usr/lib/qubes/qrexec-client-vm '
-                    '{} test.Argument+argument'.format(self.testvm2.name)))
+                    '{} test.Argument+argument'.format(self.testvm2.name),
+                    stderr=None))
 
         self.assertEqual(stdout, b'specific: argument')
 
@@ -557,7 +573,8 @@ def test_084_qrexec_service_argument_extra_env(self):
         with self.qrexec_policy('test.Argument', self.testvm1, self.testvm2):
             stdout, stderr = self.loop.run_until_complete(
                 self.testvm1.run_for_stdio('/usr/lib/qubes/qrexec-client-vm '
-                    '{} test.Argument+argument'.format(self.testvm2.name)))
+                    '{} test.Argument+argument'.format(self.testvm2.name),
+                    stderr=None))
 
         self.assertEqual(stdout, b'test.Argument+argument argument')