[FIX JENKINS-25505] cannot resolve host exception
Revert "[JENKINS-25676]: disable creation of vCard/avatar because of what looks like a bug in Smack 4.0.5"

This reverts commit ffa8fbf502918a0581fa1fa6db595e589dbed352.
[FIX JENKINS-25676]: added 5 minute interval keep-alive pings to avoid
disconnection from (buggy) servers