shill: manager: send a reply to Enable/Disable Technology even if no devices

Send a reply to Enable/Disable Technology even if no devices need to
be disabled or enabled.

BUG=none
TEST=shill on vm. run test-flimflam enable cellular.  command does not timeout.

Change-Id: I3892b80cc0281fcc6aa530630897af44098430bd
Reviewed-on: https://gerrit.chromium.org/gerrit/22598
Commit-Ready: Jason Glasgow <jglasgow@chromium.org>
Reviewed-by: Jason Glasgow <jglasgow@chromium.org>
Tested-by: Jason Glasgow <jglasgow@chromium.org>
diff --git a/mock_device.h b/mock_device.h
index beb3c27..8f0573e 100644
--- a/mock_device.h
+++ b/mock_device.h
@@ -30,6 +30,9 @@
   MOCK_METHOD2(Stop, void(Error *error,
                           const EnabledStateChangedCallback &callback));
   MOCK_METHOD1(SetEnabled, void(bool));
+  MOCK_METHOD3(SetEnabledPersistent, void(bool enable,
+                                          Error* error,
+                                          const ResultCallback &callback));
   MOCK_METHOD1(Scan, void(Error *error));
   MOCK_CONST_METHOD1(TechnologyIs,
                      bool(const Technology::Identifier technology));