Added support to explicitly manage task definitions be revision. If the
revision expectations of the ansible task cannot be met, an error is
thrown.
If revision is not explicitly specified, enhanced module to be
idempotent with respect to task definitions. It will search for an
active revision of the task definition that matches the containers and
volumes specified. If none can be found, a new revision will be created.
Some do not use the json module directly so don't need import json.
Some needed to fallback to simplejson with no traceback if neither was installed
Fixes#1298
