Properly template list of hosts in playbooks.

In playbooks, hosts can be a YAML list. We templated the list before
converting it to a semicolon-separated string, which actually templated its
repr. This converts to a string first. A basic unit test is included.

test/TestPlayBook.py

@@ -172,3 +172,16 @@ class TestPlaybook(unittest.TestCase):
        print data
        assert data.find("ears") != -1, "template success"
 
+   def test_yaml_hosts_list(self):
+       # Make sure playbooks support hosts: [host1, host2]
+       # TODO: Actually run the play on more than one host
+       test_callbacks = TestCallbacks()
+       playbook = ansible.playbook.PlayBook(
+           playbook=os.path.join(self.test_dir, 'hosts_list.yml'),
+           host_list='test/ansible_hosts',
+           stats=ans_callbacks.AggregateStats(),
+           callbacks=test_callbacks,
+           runner_callbacks=test_callbacks
+       )
+       play = ansible.playbook.Play(playbook, playbook.playbook[0])
+       assert play.hosts == ';'.join(('host1', 'host2', 'host3'))

test/hosts_list.yml

@@ -0,0 +1,5 @@
+# Test that playbooks support YAML lists of hosts.
+---
+- hosts: [host1, host2, host3]
+  tasks:
+  - action: command true