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
Merge branch 'failed_when' of https://github.com/hnakamur/ansible into hnakamur-failed_when
Updated CHANGELOG for the failed_when feature