We used to add the Ubuntu image to the list of
images to download during the glance bootstrap
in one of our test script. This image is mostly
used for debugging and when cirros is incompatible
with infra VMs. So let's add glance values override
file specifically for this and enable it only when
necessary.
Change-Id: I5c10dac4826c3ea10327e4934bbeab27b54877e2
97099183e4