Fix and add a test case for IPv6
Fix and add a test case for IPv6

Fixing and adding a test case in relation to the eventlet ipv6 fix
in patch set 23 (https://review.openstack.org/#/c/101079/).

  * pre-import eventlet for test case test_evnetlet_no_dnspython,
    which wasn't actually importing eventlet like it described.
  * add case test_no_evnetlet_no_dnspython

Change-Id: I55c40ed735781862f8352afb917058bf475d16fe
(cherry picked from commit 9447d37d653d87c89a1daf8f5affe41269beffbd)

redhat-openstack/glance,redhat-openstack/glance