[ FLOC-1010] Improvements to the release process documentation

Fixes https://clusterhq.atlassian.net/browse/FLOC-1010 (edit and https://clusterhq.atlassian.net/browse/FLOC-1049)
We should instead suggest using `clusterhq/fedora20-updated` or the like. The development machine already has a bunch of requirements installed, so doesn't seem like a good test target.