<oo-admin-check-sources.py> Bug 1025560 - Store repo conflict resolutionand guarantee uniqueness before updating priorities

Non-blessed repos which provide a package that conflicted with
multiple blessed repos would result in multiple lines of advice being
output. This commit adds a dictionary - `resolved_repos` - where
pending repo priority conflicts are stored for later resolution. The
dictionary is keyed by repoid, guaranteeing uniqueness, preventing the
multiple redundant lines of advice.