CLI support for queue existence and metadata operations

This patch extends the queues operation supported by the CLI.
It also renames some of the previously added features to make
them more consistent with their behaviour.

Features added:
- Check queue existence
- Set queue metadata
- Get queue metadata
- Get queue stats

Some examples:
	$ openstack queue exists myqueue
	$ openstack queue set metadata '{"key":"value"}'
	$ openstack queue stats myqueue

The above assumes Keystone is installed and has an endpoint
configured for Zaqar. In order to bypass this in a non-Keystone
based deployment, the user can pass Marconi's url manually:

    $  openstack --os-token test
                 --os-url http://127.0.0.1:8888
		 queue exists myqueue

Partially-Implements: blueprint cli
Co-Author-by: Victoria Martínez de la Cruz <victoria@vmartinezdelacruz.com>
Change-Id: Idcc455a04b12a6e55ed077d221f6d3ca2ef055f8
Merge "CLI support for queue existence and metadata operations"