Add failed_when module variable.

Implementation note: Ternery operator trick for python prior to 2.5 is used.
(test and [when_true_value] or [when_false_value])[0]
http://stackoverflow.com/questions/394809/ternary-conditional-operator-in-python#comment1466794_394887

test/TestPlayBook.py

@@ -474,6 +474,34 @@ class TestPlaybook(unittest.TestCase):
 
        assert utils.jsonify(expected, format=True) == utils.jsonify(actual,format=True)
 
+   def test_playbook_failed_when(self):
+       test_callbacks = TestCallbacks()
+       playbook = ansible.playbook.PlayBook(
+           playbook=os.path.join(self.test_dir, 'playbook-failed_when.yml'),
+           host_list='test/ansible_hosts',
+           stats=ans_callbacks.AggregateStats(),
+           callbacks=test_callbacks,
+           runner_callbacks=test_callbacks
+       )
+       actual = playbook.run()
+
+       # if different, this will output to screen
+       print "**ACTUAL**"
+       print utils.jsonify(actual, format=True)
+       expected =  {
+           "localhost": {
+               "changed": 2,
+               "failures": 1,
+               "ok": 2,
+               "skipped": 0,
+               "unreachable": 0
+           }
+       }
+       print "**EXPECTED**"
+       print utils.jsonify(expected, format=True)
+
+       assert utils.jsonify(expected, format=True) == utils.jsonify(actual,format=True)
+
 
    def test_playbook_always_run(self):
       test_callbacks = TestCallbacks()

test/playbook-failed_when.yml

@@ -0,0 +1,15 @@
+---
+- hosts: all
+  connection: local
+  gather_facts: False
+
+  tasks:
+  - action: shell exit 0
+    register: exit
+    failed_when: not exit.rc in [0, 1]
+  - action: shell exit 1
+    register: exit
+    failed_when: exit.rc not in [0, 1]
+  - action: shell exit 2
+    register: exit
+    failed_when: exit.rc not in [0, 1]