Fix JENKINS-25676 (and also JENKINS-25222)

Instead of going with an server specific solution, re-use Smack's PingManager for all connections.

Right now it's not possible to change the server ping interval. This feature can be added in a later version. Right now the change should address JENKINS-25676 and JENKINS-25222, but would be great if the affected users could confirm that.
Yeah, but HipChat was currently already using a 60 sec interval.
So changing this to 5 minutes to all, would have resulted in a regression for HipChat users