Revert "report message even if no action is specified"

This reverts commit 031e23f72318c65346f88e3cad3989eed4f7368b
and commit 9ba206866499cbe1bbda4fb5e1b4fabbbc82e934.

This breaks the ability to have silent pipelines.

Instead, how about the following:

  pipelines:
  - name: postmerge
    manager: IndependentPipelineManager
    ...
    success:
      force-message: true

That should work without any additional code.

Change-Id: I0d15b8fcb678a36c46205693ba9a6756ec6a076f
Reviewed-on: https://review.openstack.org/29180
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Antoine Musso <hashar@free.fr>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins