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



git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@423462 f38db490-d61c-443f-a65b-d21fe96a405b