UPSTREAM: selinux: refactor sidtab conversion

This is a purely cosmetic change that encapsulates the three-step sidtab
conversion logic (shutdown -> clone -> map) into a single function
defined in sidtab.c (as opposed to services.c).

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Stephen Smalley <sds@tycho.nsa.gov>
[PM: whitespaces fixes to make checkpatch happy]
Signed-off-by: Paul Moore <paul@paul-moore.com>

(cherry picked from commit 5386e6caa6711407182573e2b0344fe908b0fbcc)
Change-Id: If23e6e40bd0c920cac090c2e9379d148d3ac6ca3
Bug: 140252993
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>