Fix to resubscribe to salesforce pushtopics every 2 hours

Salesforce pushtopic drops the connection after every 2 hours. mule-sfdc-connector does reconnect at that point but it does not resubscribe. Hence, it does not receive updates from sfdc pushtopics after 2 hours. 
Made changes so that mule re-subscribes every 2 hours and so continues getting updates from sfdc.