Now we have multiple remotes that can be enabled or changed at runtime we need
to do several things better:
* Only load components from remotes that are enabled
* Only load a component if a higher priority remote has not already added it
Rather than just appending all recieved metadata into one big XML file, save
the original metadata .xml.gz files in /var/lib/fwupd/remotes.d and only load
them in the correct priority order if the remote is known and enabled.
Remove the old /var/cache/app-info/xmls/fwupd.xml file, also noting it wasn't
really a cache file at all but actually something quite important.
This also moves the tests into one file as gnome-desktop-testing-runner
intentionally randomizes the order and runs them in parallel where allowed.
Since tests like get-updates have to be run after the metadata injection simply
put these into one test that calls a simple script.
