rest_api/channels: Fix multiple issues with create and dial

* We weren't properly subscribing to the channel and it's originator
  on create.
* We weren't doing a publish_dial after calling ast_call on dial.
* We weren't calling depart_bridge when a channel left the dial bridge.

The first 2 issues were causing events to not be generated and the third
was actually causing channels to not get properly destroyed when hung up.

Together these 3 issues were causing the new
rest_apichannels/create_dial_bridge tests to fail.

As a result of the fixes, the cdr state machine had to be slightly
tweaked to allow bridge leave events without asserting and the tests
themselves had to be updated to account for the channels now cleaning
themselves up.

Change-Id: Ibf23abf5a62de76e82afb4461af5099c961b97d8