utils/revent: stop recording fix.

It seems that occasionally an inclomplete recording file is pulled. Add
a one-second (target time) delay to allow SIGINT to be properly handled
and recording to be updated, followed by a sync to ensure the file has
been written.

wa/utils/revent.py

@@ -281,6 +281,8 @@ class ReventRecorder(object):
 
     def stop_record(self):
         self.target.killall('revent', signal.SIGINT, as_root=self.target.is_rooted)
+        self.target.sleep(1)
+        self.target.execute('sync')
 
     def replay(self, revent_file, timeout=None):
         self.target.killall('revent')