Gsid should behave more like a normal service.

This patch makes the following changes to gsid:
 - It now runs on startup and is no longer a one-shot service.
 - /data/gsi is now created via init, with the appropriate permissions.
 - gsi_tool no longer starts/stops gsid.
 - /metadata/gsi is readable by the system group, so system_server can
   read /metadata/gsi/booted.

Bug: 122556707
Test: manual test
Change-Id: I08c0c6e9a155a0dea113c8535e71bda5aeda0ff6
4 files changed