[SYNCOPE-574] null-safe ConnConfProperty.compareTo()

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_2_X@1633201 13f79535-47bb-0310-9956-ffa450edef68
[SYNCOPE-574] Merge from 1_2_X

git-svn-id: https://svn.apache.org/repos/asf/syncope/trunk@1633205 13f79535-47bb-0310-9956-ffa450edef68