nm provider: Refactor the down action of network connection

When deactivating a profile in libNM, we should:

 * Check `NM.ActionConnection` existence
 * Check `NM.ActionConnection.props.state` not DEACTIVATED
 * Use signal `state-changed` of `NM.ActionConnection`.
 * Only invoke `NM.Client.deactivate_connection_async()` if not
   in DEACTIVATING state.
 * Ignore `NM.ManagerError.CONNECTIONNOTACTIVE` error.

This patch also introduced a new class `NetworkManagerProvider`
in `module_utils/network_lsr/nm`:

 * Independent from Ansible but need to use absolute import due to
   limitation of ansible 2.8.
 * Provide sync function wrapping async calls of libNM.
 * Use stable logging method of python.
 * Only load this module when provider is nm.

This patch also changed how logging is handling in
`Cmd_nm.run_action_down()` as initial step on isolate ansible log
mechanism from provider module.

By moving provider codes to `module_utils` folder, we can eventually
simplify the bloated `library/network_connections.py`.

Signed-off-by: Gris Ge <fge@redhat.com>

tests/integration/test_ethernet.py

@@ -92,7 +92,25 @@ def _get_ip_addresses(interface):
     return ip_address.decode("UTF-8")
 
 
-def test_static_ip_with_ethernet(testnic1, provider):
+@pytest.fixture
+def network_lsr_nm_mock():
+    with mock.patch.object(
+        sys,
+        "path",
+        [parentdir, os.path.join(parentdir, "module_utils/network_lsr/nm")] + sys.path,
+    ):
+        with mock.patch.dict(
+            "sys.modules",
+            {
+                "ansible": mock.Mock(),
+                "ansible.module_utils": __import__("module_utils"),
+                "ansible.module_utils.basic": mock.Mock(),
+            },
+        ):
+            yield
+
+
+def test_static_ip_with_ethernet(testnic1, provider, network_lsr_nm_mock):
     ip_address = "192.0.2.127/24"
     connections = [
         {