Several nm-device-*.c files apparently originally used
nm-device-ethernet.c as a template, but missed a reference to "eth" in
class_init.

_nm_client_is_object_path() had been copied from
g_variant_is_object_path() with a note that it should be replaced when
we depended on GLib > 2.24, but it got missed when we actually updated
the dependency. Fix it now. (Also fix a nearby typo.)

Test that the code to track whether NetworkManager is running works
correctly.

NMObjectCache was assuming there would never be more than one object
with the same path, but since NMClient is an NMObject, it was getting
cached too, so if you created two clients and then unreffed one of
them, it's possible the wrong one could get left in the cache, causing
a crash the next time the other one called nm_object_cache_clear().

Fix this by only adding NMObjects to the cache in the codepaths where
we also check to see if the object was already in the cache.

(This also means we can remove the "except" argument to
nm_object_cache_clear(), since the NMClient won't be cached any more.)

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.

Use "TESTS = tests-nm-client test-remote-settings-client" rather than
overriding "check-local".

Add a script "libnm-test-launch.sh" that will handle redirecting the
test via dbus-launch if needed.

Rather than passing the path to the test service on the command line,
compile it into the test programs.

(Among other things, this makes it easier to run the test directly
from the command line.)

clang warns:

    make[4]: Entering directory `./NetworkManager/libnm-glib'
      CC       libnm_glib_la-nm-remote-connection.lo
    nm-remote-connection.c:77:3: error: redefinition of typedef 'RemoteCall' is a C11 feature [-Werror,-Wtypedef-redefinition]
    } RemoteCall;
      ^
    nm-remote-connection.c:67:27: note: previous definition is here
    typedef struct RemoteCall RemoteCall;
                              ^

Signed-off-by: Thomas Haller <thaller@redhat.com>

- register a weak references and ensure that the connection
  is removed when expected.

- disconnect the vis_new_connection_cb() handler

Signed-off-by: Thomas Haller <thaller@redhat.com>