Template upload: revamp template name, use version file

If version file exists, it will be used. Now it'll look like this:

cfme-5.2.4.2-0624
cfme-nightly-5.3.0.0-15.el6cf.alpha7-0623
miq-nightly-201406242000
`template_name` behaves as though the image name will always be lowercase, but I don't see anything ensuring that it will be. Am I missing that, or would a `.lower()` be useful here?