Headless: fix locking work profile with separate challenge on power button

SystemUI is querying the profile of its own running user, but in
headless system user mode this should really be the current foreground
user.

Also fix a bug in DevicePolicyManager where device lock timeout is
pushed to the wrong user.

Bug: 265021591
Test: manual run of the CtsVerifier test
Change-Id: I714cda9040b8712df6753a9d37e8c293fe527ad9