libnm-glib: make test-networkmanager-service.py automatically exit with its parent

test-nm-client.c and test-remote-settings-client.c were using their
own assertion macros so they could kill the test service on assertion
failure. Except that some new code didn't get the memo and used the
g_assert* macros. Not to mention that sometimes the tests would crash
outside of an assertion macro.

We can make test-networkmanager-service.py notice that its parent has
crashed by opening a pipe between them and taking advantage of the
fact that the pipe will be automatically closed if the parent crashes.
So then test-networkmanager-service.py just has to watch for that, and
exit if the pipe closes.

Then that lets us drop the test_assert* macros and just use g_assert*
instead.

tools/test-networkmanager-service.py

@@ -858,6 +858,9 @@ class Settings(dbus.service.Object):
 
 ###################################################################
 
+def stdin_cb(io, condition):
+    mainloop.quit()
+
 def quit_cb(user_data):
     mainloop.quit()
 
@@ -872,7 +875,11 @@ def main():
     if not bus.request_name("org.freedesktop.NetworkManager"):
         sys.exit(1)
 
-    # quit after inactivity to ensure we don't stick around if tests fail
+    # Watch stdin; if it closes, assume our parent has crashed, and exit
+    io = GLib.IOChannel.unix_new(0)
+    io.add_watch(GLib.IOCondition.HUP, stdin_cb)
+
+    # also quit after inactivity to ensure we don't stick around if the above fails somehow
     GLib.timeout_add_seconds(20, quit_cb, None)
 
     try: