Move libnm-glib's test-fake-nm.py and test-remote-settings-service.py
to tools/, merge them together into a single program, and fix a few
bugs (notably some missing signal emissions in the Settings service).

Although they are currently only used by libnm-glib's tests, they are
generic enough that they could be used by other code in the future
(and in particular, they will be used by libnm's tests as well).