rpmostree: Cache rpm -qa between runs, don't commit if packageset is unchanged

At the moment, a lot of RPM content has files whose content derives
from timestamps (like .pyc files).  We really don't need to do another
commit to the repository if it's just these files which changed.

Fix this by caching the package list at the rpm-ostree level, and
don't commit if it hasn't changed.
fedostree/web: Correct deploy commands

We need them to include the remote so that upgrade works.