Fix ansible tasks on python3
Fix ansible tasks on python3

The ansible task would be reading the stdout from pipe to know when
that finished. The stopping sentinel for that reading was a binary empty
That was failing on python3 making it hang and consume 100% cpu
Changed the inter sentinel to empty space that works for both
python 2 and 3.

The issue is mentioned on a downstream bug
https://bugzilla.redhat.com/show_bug.cgi?id=1686397

Change-Id: If12c573430ddbd13243003fc16d7cdabf394fb7b

openstack/tripleo-common,openstack/tripleo-common