Fix home can not be started while instrumenting

We don't want to automatically start home activities while
the home app is being instrumented because it prevents home
activities unexpectedly resumed during testing.

We should still allow launching home activities if requested
(e.g. starting home activity when home key pressed).

Bug: 118891218
Test: atest TaplTests
Test: atest ActivityStackSupervisorTests
Test: atest ActivityManagerMultiDisplayTests

Change-Id: Ia362f875d38748a3dea40b5788a4d86bcc68392c