Update Authentication UI strings to match Android UX spec.

Test: Updated UI test, passing.
Bug: 36869182
Bug: 36869091
Change-Id: Ib3538c6607a852d436469b34d94b66f3534e9083
(cherry picked from commit 62d54bac2fefe7d87a750af8e94a8bd99ab88510)
3 files changed