fix(controller): format command before creating container

The self._command_announceable() check was called inline with code
that formatted the container's command, so no announcer would be
created since the command showed up as "start {c_type}" literally.
The _command property is only referenced in this code.

TESTING: First verify that a Procfile-based app fails to start its announce container on Deis master code. Then check out this branch, build and restart deis-controller, and push the app again--"Welcome to Nginx" should be replaced by "Welcome to Deis."