This reworks the gerrit testing slightly to give some broader
coverage.
It sets up ssh keys for the user; not really necessary but can be
helpful when interacting on a held host.
It sets up groups and verification labels just so Zuul can comment
with -2/+2; again this is not really necessary, but makes things a
little closer to production reality.
We make multiple changes, so we can better test navigating between
them. The change comments are updated to have some randomness in them
so they don't all look the same. We take screen shots of two change
pages to validate the navigation between them.
Change-Id: I60b869e4fdcf8849de836e33db643743128f8a70
9f4cbcfbc2