Add hwservice_contexts and support for querying it.

hwservicemanager can check hwservice_contexts files
both from the framework and vendor partitions.

Initially, have a wildcard '*' in hwservice_contexts
that maps to a label that can be added/found from
domain. This needs to be removed when the proper policy
is in place.

Also, grant su/shell access to hwservicemanager list
operations, so tools like 'lshal' continue to work.

Bug: 34454312
Test: Marlin boots
Change-Id: I3a02d97a82458692b528d85c1b8e78b6f82ea1bc