main/test: Fix race condition between AMI topic and Test Suite topic

This patch fixes a race condition between the raising of test AMI events (which
drive many tests in the Asterisk Test Suite) and other AMI events. Prior to
this patch, the Stasis messages published to the test topic were not forwarded
to the AMI topic. Instead, the code in manager had a dedicated handler for test
messages that was independent of the topics forwarded to the AMI topic. This
results in no synchronization between the test messages and the rest of the
Stasis messages published out over AMI. In some test with very tight timing
constraints, this can result in out of order messages and spurious test
failures. Properly forwarding the Test Suite topic to the AMI topic ensures
that the messages are synchronized properly.

This patch does that, and moves the message handling to the Stasis definition
of the Test Suite message in test.c as well.

Review: https://reviewboard.asterisk.org/r/4221/
........

Merged revisions 428945 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@428946 f38db490-d61c-443f-a65b-d21fe96a405b