Integration with Zaqar

After trying, I found it is not easy to integrate zaqarclient in mistral, as implementation of zaqarclient is totally different with many other client projects. For example, for almost other client projects, there are always operable objects inside the Client class, so we can get public methods of them, to decide what methods we can invode as mistral action, and their corresponding input params. Please see source code below:
python-muranoclient: https://github.com/openstack/python-muranoclient/blob/master/muranoclient/v1/client.py#L42-L62
python-ceilometerclient: https://github.com/openstack/python-ceilometerclient/blob/master/ceilometerclient/v2/client.py#L66-L84
python-glanceclient: https://github.com/openstack/python-glanceclient/blob/master/glanceclient/v2/client.py#L45-L68
....

However, we can't use the same mechanism for zaqarclient unless zaqar team make some changes for adaptation.
https://github.com/openstack/python-zaqarclient/blob/master/zaqarclient/queues/v1/client.py

--xylan 2015.12.05

Gerrit topic: https://review.openstack.org/#q,topic:bp/mistral-zaqar-integration,n,z

Addressed by: https://review.openstack.org/275096
    Implement basic Zaqar queue operations