Normalize user active logic across Location APIs

Adds additional logic for location requests coming from the system
server, such that those requests may allowed so long as location is on
for the current user, even if the system user has location disabled.
Even though the system server runs under the system user, it may need
to service requests from or on behalf of other users.

Test: presubmits + manual
Change-Id: Ic9d7762e75fc930b7d26f1d1bf20b272d562939c