Don't accumulate ansible output uselessly
Don't accumulate ansible output uselessly

To not overload mistral, we often call the ansible playbook action with
"trash_output". When that's the case, we can discard stdout immediately,
instead of accumulating it and then discarding it.

Change-Id: Ia3d05d716a8e0a1665f9b9310f7d25370bbcdf8d

openstack/tripleo-common,openstack/tripleo-common