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.
HipChat server unfortunately times out after 150s of inactivity, so using 5 minute pings for all servers won't work.
See http://help.hipchat.com/knowledgebase/articles/64377-xmpp-jabber-support-details