1) Combined settings page should finish() when losing foreground
(but not if fingerprint or face settings are launched from it)
2) Challenge should be generated when entering FaceSettings or
FingerprintSettings each time. This allows us to leave the existing
revokeChallenge paths in FaceSettings and FingerprintSettings.
Fixes: 186257202
Test: Manual
Change-Id: I1b6452f787279001a71628f220c01fcb86b88f3d
The combined biometrics settings has been integrating face and
fingerprint authentication together, so the confirming credential flow
has to be invoked before entering biometrics settings page.
Bug: 183449119
Test: manual
Change-Id: I3c0d059241cb10a254868c2e388c4d3b20305b10