Fix start_app timeout mechanism which assumes _is_app_running() retur… (

#186)

* Fix start_app timeout mechanism which assumes _is_app_running() returns immediately.
Previously, this was looping for
wait_time x (1+_SOCKET_CONNECTION_TIMEOUT+_SOCKET_READ_TIMEOUT) seconds
instead of
wait_time x (1) seconds

mobly/controllers/android_device_lib/jsonrpc_client_base.py

@@ -175,19 +175,21 @@ def start_app(self, wait_time=APP_START_WAIT_TIME):
         """Starts the server app on the android device.
 
         Args:
-            wait_time: float, The time to wait for the app to come up before
-                       raising an error.
+            wait_time: int, The minimum number of seconds to wait for the app
+                to come up before raising an error. Note that _is_app_running()
+                may take longer than wait_time.
 
         Raises:
             AppStartError: When the app was not able to be started.
         """
         self.check_app_installed()
         self._do_start_app()
-        for _ in range(wait_time):
-            time.sleep(1)
+        expiration_time = time.time() + wait_time
+        while time.time() < expiration_time:
             if self._is_app_running():
                 self._log.debug('Successfully started %s', self.app_name)
                 return
+            time.sleep(1)
         raise AppStartError('%s failed to start on %s.' %
                             (self.app_name, self._adb.serial))