Fact gathering on a second play against the same hosts should not be implicitly…

Fact gathering on a second play against the same hosts should not be implicitly off since this is an undocumented beheavior and potentially
rather unwanted when a play could change a fact.

gather_facts: True/False can still be explicitly used per play.

Reverts 564a212b

lib/ansible/playbook/play.py

@@ -114,7 +114,7 @@ class Play(object):
         self.sudo             = ds.get('sudo', self.playbook.sudo)
         self.sudo_user        = ds.get('sudo_user', self.playbook.sudo_user)
         self.transport        = ds.get('connection', self.playbook.transport)
-        self.gather_facts     = ds.get('gather_facts', None)
+        self.gather_facts     = ds.get('gather_facts', True)
         self.remote_port      = self.remote_port
         self.any_errors_fatal = utils.boolean(ds.get('any_errors_fatal', 'false'))
         self.accelerate       = utils.boolean(ds.get('accelerate', 'false'))