Prepare CaptivePortalLogin for system_current

Includes small changes to stop using non-SystemApi endpoints.

Test: make CaptivePortalLogin
Test: flashed, login works, SSL certificate invalid flow works
Bug: 112869080
Merged-In: Ic6ce98942959705ea7ef14a7a62d33e3abf7eb72
Change-Id: Ie7ea3bab6aa8629ce4c111adee0c0699d95d4b0e
8 files changed