Revert "Revert "Only update default home when the preferred home activity is modified.""

To avoid the race condition when other preferred activities are being
configured while home role is being set.

This reverts commit d30570e2.

Reason for revert: Resubmission after fix
Bug: 178191941
Test: presubmit
Change-Id: Ib9777aba92462eec1d7c595833a86cfeddc02c1b