Add test to shelve the paused server: bug# 1745529

This commit adds test to shelve the paused instance.
As per Nova doc[1], user should be able to shelve the instance
even it is in paused state but this is not happening as per
mentioned bugs and there was no coverage of this scenario in tempest.

..1 https://developer.openstack.org/api-ref/compute/#shelve-server-shelve-action
Related-Bug: #1745529

Depends-On: I8ca25d9847d50001fbe8513a6c1dba8b697c24e4
Change-Id: Id5782583511e5601c1bc7fe99db7d6d4c479db11
1 file changed