Add subscription state test events.

These are needed for a set of batched notification RLS tests that are
about to be committed to the testsuite.

Review: https://reviewboard.asterisk.org/r/3967
........

Merged revisions 423462 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@423463 65c4cc65-6c06-0410-ace0-fbb531ad65f3