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

tripleo_common/actions/ansible.py

@@ -567,7 +567,7 @@ class AnsiblePlaybookAction(base.TripleOAction):
                 start = time.time()
                 stdout = []
                 lines = []
-                for line in iter(process.stdout.readline, b''):
+                for line in iter(process.stdout.readline, ''):
                     lines.append(line)
                     if not self.trash_output:
                         stdout.append(line)