improved Sync Tasks migration during core-upgrade

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_2_X@1625899 13f79535-47bb-0310-9956-ffa450edef68
Merge from branch 1_2_X

git-svn-id: https://svn.apache.org/repos/asf/syncope/trunk@1625901 13f79535-47bb-0310-9956-ffa450edef68