Delete old images before uploading a new one to glance

The openstack client that the image upload in devstack now uses
(I96cef118daf931b648c0483525ac7d2287fec2e0) fails when trying to
upload another image having the same name into the glance catalog.

This change cleans up any older images that may exist in the catalog
before uploading the new image as part of kick-start.

Change-Id: I5f8c3172ae0e83dd5393eaf70afdb5d2ba7075d0
Closes-bug: 1357472
Merge "Delete old images before uploading a new one to glance"