OsuLogin: Take the UI style from CaptivePortalLogin App

1) Currently OsuLogin application has different color and style
with CaptivePortalLogin.
It is better to have same style with CaptivePortalLogin from user perspective.
2) remove NET_CAPABILITY_TRUSTED cap to catch the disconnect event for
ehpemeral network which was set in ag/5054830

Bug: 118454343
Test: live test with Passpoint R2 service provider AP
Change-Id: I4121d56b843d0ff2ebebb4bd4a063f2a5c5a0dd8
Signed-off-by: Ecco Park <eccopark@google.com>