fixes #1767 parsing serial from extra_vars

lib/ansible/playbook/__init__.py

@@ -406,7 +406,7 @@ class PlayBook(object):
             # do N forks all the way through before moving to next
             while len(all_hosts) > 0:
                 play_hosts = []
-                for x in range(play.serial):
+                for x in range(int(play.serial)):
                     if len(all_hosts) > 0:
                         play_hosts.append(all_hosts.pop())
                 serialized_batch.append(play_hosts)

lib/ansible/playbook/play.py

@@ -75,7 +75,7 @@ class Play(object):
         self.transport    = ds.get('connection', self.playbook.transport)
         self.tags         = ds.get('tags', None)
         self.gather_facts = ds.get('gather_facts', None)
-        self.serial       = ds.get('serial', 0)
+        self.serial       = utils.template_ds(basedir, ds.get('serial', 0), self.vars)
 
         if isinstance(self.remote_port, basestring):
             self.remote_port = utils.template(basedir, self.remote_port, self.vars)