* Port rally.task.engine to use EnvManager instead of Deployment
* Rename method `set_deployment` of `rally.common.objects.Verifier`
to `set_env`. It can be done in backward incompatible way, since the
original method should be called only from rally.api
* Extend `rally.common.objects.Verifier` with `env` property
* Move OpenStackCredential under dict parenthood. object like style
makes things too complicated. The simple dict should give more
transparency. As for backward compatibility old-behaviour is kept.
* Call `check_helth` method of EnvManager from TaskEngine instead of
hardcoded for openstack `verify_connection` method.
* Remove methods `get_validation_context` and `verify_connection` from
OpenStackCredential. It should not be called anywhere.
Change-Id: I76608deaefc68dbd5a99a3339584c9cf70e16ba0
8c13c9d64f