cellular: Update network_3GDormancyDance to use mm.py from autotest

This CL updates the network_3GDormancyDance test to use the mm.py from
autotest_lib.client.cros.cellular instead of the one from
shill-test-scripts as the latter is deprecated and replaced by the
former.

BUG=chromium:404003
TEST=Run network_3GDormancyDance test.

Change-Id: I523bb88ec1bb79b37607c0b1e0fde4cedb44b610
Reviewed-on: https://chromium-review.googlesource.com/212571
Tested-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
1 file changed