Secure random string

git-svn-id: https://svn.apache.org/repos/asf/syncope/branches/1_1_X@1486918 13f79535-47bb-0310-9956-ffa450edef68
merge from 1_1_X to close [SYNCOPE-374]

git-svn-id: https://svn.apache.org/repos/asf/syncope/trunk@1486919 13f79535-47bb-0310-9956-ffa450edef68