Add timeout waiting for response from FreeSWITCH when sending ESL command

 - When waiting for a response from FS after sending an ESL command and the ESL connection disconnects,
   the sending thread will be blocked as the trigger for it to unblock is the response from FS which never
   comes.

   Add a 30 second timesout waiting for response and give up to go send a new FS ESL command.