tests/test_cel: Unlock bridge on off nominal paths

If the test fails due to memory allocation errors, we may as well attempt to
unlock the bridge on the way out.
........

Merged revisions 427927 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@427932 f38db490-d61c-443f-a65b-d21fe96a405b