Added images support and existing config support

This adds the support of auto configuring images to be used by
tempest by either using existing images in glance or in case they
do not exist, download the cirros images and register them.
Also, added the option of specifing a config file instead of
relying on the sample

Change-Id: I436d2a75706fdaa294a92d0fd38ea3269c776e8c
1 file changed