Fix PRESUBMIT.py for build/android/buildbot

The code was making a call to android_commands.py, which
relied on a copy of adb existing in the path.  The CQ
bot does not have third_party/android_tools, and in general
it seems advantageous to not require a full checkout for
syntax checks.

NOTRY=True

Review URL: https://chromiumcodereview.appspot.com/11883019

git-svn-id: http://src.chromium.org/svn/trunk/src/build@176723 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/buildbot/bb_device_steps.py

@@ -98,9 +98,13 @@ def RebootDeviceSafe(device):
 def RebootDevices():
   """Reboot all attached and online devices."""
   buildbot_report.PrintNamedStep('Reboot devices')
+  # Early return here to avoid presubmit dependence on adb,
+  # which might not exist in this checkout.
+  if TESTING:
+    return
   devices = android_commands.GetAttachedDevices()
   print 'Rebooting: %s' % devices
-  if devices and not TESTING:
+  if devices:
     pool = multiprocessing.Pool(len(devices))
     results = pool.map_async(RebootDeviceSafe, devices).get(99999)