Always update cached copy of authenticatorId.

This fixes a bug where the cached copy of authenticatorId
was incorrect immediately after enrolling a new fingerprint.
During enroll, the authenticatorId is changed and needs to be updated.
The fix is to always get the new authenticatorId when we
call setActiveGroup(), which happens during every new

Fixes bug 28606914

Change-Id: I8b2d3afe67b3677b6e4516a550d874d9c2e426cd