Adds support for SSL verification when ``OPENSTACK_SSL_CACERT`` is set.
Explicitly skips verification if ``OPENSTACK_SSL_NO_VERIFY`` is set.
This also switches to Session-based instantiation for the Blazar client,
away from the deprecated url+token method.
Closes-Bug: #2045281
Change-Id: I94aad7590b1e42ddfa1a20fdb184ca4d73587cd6