tests: use libnm via pygobject in tools/test-networkmanager-service.py

tools/test-networkmanager-service.py is our NetworkManager stub server.

NetworkManager uses libnm(-core) heavily, for example to decide whether
a connection verifies (nm_connection_verify()) and for normalizing
connections (nm_connection_normalize()).

If the stub server wants to mimic NetworkManager, it also must use these
function. Luckily, we already can do so, by loading libnm using python
GObject introspection.

We already correctly set GI_TYPELIB_PATH search path, so that the
correct libnm is loaded -- provided that we build with introspection
enabled.

We still need to gracefully fail, if starting the stub server fails.
That requries some extra effort. If the stub server notices that
something is missing, it shall exit with status 77. That will cause
the tests to g_test_skip().

tools/test-networkmanager-service.py

@@ -3,8 +3,18 @@
 
 from __future__ import print_function
 
-from gi.repository import GLib
 import sys
+
+import gi
+from gi.repository import GLib
+
+try:
+    gi.require_version('NM', '1.0')
+    from gi.repository import NM
+except Exception as e:
+    print("Cannot load gi.NM: %s" % (str(e)))
+    sys.exit(77)
+
 import dbus
 import dbus.service
 import dbus.mainloop.glib