Make tempfile unreadable to secure

Doing it twice. Why? Because but infraspec send_file doesn't have an interface
to set mode nor owner. Also it doesn't guarantee to keep file mode when
overwriting existing file.

lib/itamae/resource/file.rb

@@ -171,7 +171,11 @@ def send_tempfile
                 end
 
           @temppath = ::File.join(runner.tmpdir, Time.now.to_f.to_s)
+
+          run_command(["touch", @temppath])
+          run_specinfra(:change_file_mode, @temppath, '0600')
           backend.send_file(src, @temppath)
+          run_specinfra(:change_file_mode, @temppath, '0600')
         ensure
           f.unlink if f
         end