Code review comment for lp:~ev/adt-image-mapper/fresh-keystone-client

It's true, I don't think we're going to be generating enough traffic to realize a huge gain from the caching. I figured it was good practice though, so I tried to preserve it. Checking for glanceclient.exc.HTTPUnauthorized is what I originally tried to do, but it doesn't come through as that exception. However, if it's true that this is fixed in the glanceclient that we just updated to, it could be that we can just revert my previous patch, keep the caching, and all will be happy.