Add option to skip and avoid captive portals.

Test: ConnectivityServiceTest updated with test cases.
Test: Manually tested against att-wifi in B42.
Bug: 30222699
Change-Id: Ibe63942da04748ab0406e24e0f44be31d47710a0
(cherry picked from commit be96da11ccb5dd500f920c3ba90d350857293b3d)
4 files changed