Selinux policy for new userspace reboot logging dir

Add userspace_reboot_metadata_file, which is written to by init,
and read by system server. System server will also handle the
deletion policy and organization of files within this directory,
so it needs additional permissions.

Test: Builds
Bug: 151820675
Change-Id: Ifbd70a6564e2705e3edf7da6b05486517413b211
6 files changed