polkitbackend: Add support for /usr/local/share/polkit-1/rules.d/*.rules
Now we support loading *.rules files from the following directories (in priority order):
This is the same behaviour as systemd, which is becoming fairly standard among system daemons. It fits in well with the OSTree approach of having /usr be provided as a read-only OS image, /var/local shared between multiple deployments of the same OS (and symlinked from /usr/local), and /etc be unique to each deployment.
Signed-off-by: Philip Withnall email@example.com