autotest: shill_proxy: Return Service on configure_service()

The Shill D-Bus API explicitly returns the configured Service path on
ConfigureService* methods. This change modifies ShillProxy to do so as
well for configure_service().

BUG=chromium:213802
TEST=`test_that $DUT network_WiFi_ProfileGUID` passes.
TEST=See TEST section for CL:2037668.

Change-Id: Ic25183c4fb89f0578bb846ae3360396edfd6d1ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2037667
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
Commit-Queue: Alex Khouderchah <akhouderchah@chromium.org>
Tested-by: Alex Khouderchah <akhouderchah@chromium.org>
diff --git a/client/cros/networking/shill_proxy.py b/client/cros/networking/shill_proxy.py
index 10fb233..575d242 100644
--- a/client/cros/networking/shill_proxy.py
+++ b/client/cros/networking/shill_proxy.py
@@ -426,11 +426,13 @@
         """Configure a service with given properties.
 
         @param config dictionary of service property:value pairs.
+        @return DBus object interface representing configured Service.
 
         """
         # Convert configuration values to dbus variant typed values.
         dbus_config = ShillProxy.service_properties_to_dbus_types(config)
-        self.manager.ConfigureService(dbus_config)
+        path = self.manager.ConfigureService(dbus_config)
+        return self.get_dbus_object(self.DBUS_TYPE_SERVICE, path)
 
 
     def configure_service_for_profile(self, path, config):