Correct the permission of checkin dir

Gmscore runs in cache group, so set the own:group of the checkin
directory to system:cache to align with other use cases. Because we
want proper user separation when accessing the dir, also provide
user id to set the correct selinux mls_level.

Bug: 197636740
Test: check selinux label, make sure checkin can access the directory.
Change-Id: Id47a2a30a2f37c204ef72a81ac2aebe4ee3a37b0