Add a method to start the captive portal login app.

Bug: 36203355
Bug: 36656914
Test: ConnectivityServiceTest (including new test) passes
Change-Id: Ide82858af67024623560ab79beea27c201b63447
Merged-In: I82a9a9a8da47870ba3f1bbef5941b37e970c844f

(cherry picked from commit 4734cdbbc38752765376aedb0d5208463674535e)
5 files changed