Add endpoint for getting provisioner queue metrics.
add docs for queue metric API.
Merge remote-tracking branch 'origin/develop' into feature/queue-statistics
Merge remote-tracking branch 'origin/develop' into feature/queue-statistics
cache the queue metrics and make sure tenant names are used
instead of ids, and update docs and changelog.
Merge remote-tracking branch 'origin/develop' into feature/queue-statistics

Conflicts:
	CHANGELOG.md
	docs/docs/source/rest/rest-links.rst
checkstyle fixes.
Merge pull request #301 from continuuity/feature/queue-statistics

Feature/queue statistics