Add post-deploy and post-rollback hooks

These replace the custom audit_broadcast_cmd code. An additional env
variable MRSK_RUNTIME is passed to them.

The audit broadcast after booting an accessory has been removed.

lib/mrsk/cli/templates/deploy.yml

@@ -25,10 +25,6 @@ registry:
 #   secret:
 #     - RAILS_MASTER_KEY
 
-# Call a broadcast command on deploys.
-# audit_broadcast_cmd:
-#   bin/broadcast_to_bc
-
 # Use a different ssh user than root
 # ssh:
 #   user: app