Android: wait for reboot.

On some devices, "reboot" is not synchronous, so the Reboot()
call and its internal waits were finishing before the device had even
started rebooting.

BUG=265425

Review URL: https://chromiumcodereview.appspot.com/22587004

git-svn-id: http://src.chromium.org/svn/trunk/src/build@216979 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/android_commands.py

@@ -350,6 +350,11 @@ class AndroidCommands(object):
     if full_reboot or not self.IsRootEnabled():
       self._adb.SendCommand('reboot')
       timeout = 300
+      retries = 1
+      # Wait for the device to disappear.
+      while retries < 10 and self.IsOnline():
+        time.sleep(1)
+        retries += 1
     else:
       self.RestartShell()
       timeout = 120