Only showKeyguard on strongAuthChanges for currUser

If strongAuth changes to a different user, we don't
want to show the keyguard based on the current
user's lockout state because this can cause
showing the keyguard multiple times.

For example, let's say there's user 0 and user 10.
Before this change, we could get into a situation where:
1. Both user 0 and user 10 are locked out.
2. Pin/pattern/password is entered successfully which
updates the strongAuth (lockout state) of both users 0 and 10.
3. SysUI receives a signal that user 10's strong auth
has been updated first; user 0's lockout state has not been
updated yet and is the current user, so this triggers
showing the keyguard (UNEXPECTED).
4. SysUI then receives a signal that user 0's strong auth
has been updated.

This CL avoids the situation at step #3 where we're showing
the keyguard before SysUI has the opportunity to receive
the update that user 0's lockout state is no longer locked out.

Test: atest KeyguardViewMediatorTest
Fixes: 331182254
Flag: EXEMPT bugfix
Change-Id: I46e0d969c64c50d8926ef38bf92811e0e79f30a5