Check system user is running process for dream logic.

This changelist ensures system user is running the process before
entering any dream related logic. This moves away from checking that
the current user is running the process, as this will not always be
true, such as when SystemUI restarts when a secondary user is running.

Fixes: 269611342
Test: atest SystemProcessConditionTest
Change-Id: I6471edaaea8dff93b0c86cb5bfee4a4cdabfd686