/dev/zero is inherited from apexd. This is required for
sh to start.
Bug: 126787589
Bug: 161563386
Test: apply GKI update
Change-Id: I8624996c129872b26d4c17242cb911b5e948d9bd
Adds proper file_contexts and domains for pre/postinstall hooks.
Allow the pre/postinstall hooks to communicate with update_engine stable
service.
Bug: 161563386
Test: apply a GKI update
Change-Id: I4437aab8e87ccbe55858150b95f67ec6e445ac1f