[Android] When running android test, try killing adb if no devices found

It randomly happens that adb devices return empty list even device
is actually connected, killing adb and restart it can fix this.

CL=https://codereview.chromium.org/24194002

build/android/adb_install_apk.py

@@ -10,6 +10,7 @@
 import optparse
 import os
 import sys
+import time
 
 from pylib import android_commands
 from pylib import constants
@@ -58,7 +59,20 @@ def main(argv):
   if len(args) > 1:
     raise Exception('Error: Unknown argument:', args[1:])
 
-  devices = android_commands.GetAttachedDevices()
+  retry_times = 5
+  retry_interval = 15
+  while retry_times > 0:
+    devices = android_commands.GetAttachedDevices()
+    if not devices:
+      print 'No connected devices found, '\
+            'kill adb server and retry in %d seconds...' % retry_interval
+      android_commands.AndroidCommands().KillAdbServer()
+      time.sleep(retry_interval)
+      retry_interval *= 2
+      retry_times -= 1
+    else:
+      break
+
   if not devices:
     raise Exception('Error: no connected devices')