cellular: Dispatch all pending events in ShillProxy.wait_for_property_in()

BUG=chromium:417397
TEST=network_3GSmokeTest

Change-Id: Ibd91bc2e64b1c80fb2732fb7a468e1109c1d1830
Reviewed-on: https://chromium-review.googlesource.com/219769
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
Commit-Queue: Thieu Le <thieule@chromium.org>
1 file changed