Respect DA policy before trying to start home

- This fixes a system crash when multiple TDAs are set up with
  a few TDAs that cannot host home.
- The system still tries to start home on all the TDAs and
  ActivityStartController fails later as the policy didn't allow.

Test: atest RootWindowContainerTests
Fix: 344010973
Change-Id: Iccf6de6b9b3be6cc4c005dc5047a9f757154aa12