scriptlets: always existence-check /etc/selinux/config
This does not work as expected with `/bin/sh` if the file does
not exist:
. %{_sysconfdir}/selinux/config &> /dev/null || true;
when run with `/bin/sh` (as opposed to `/bin/bash`) it exits 1
if the file does not exist. It exits 0 if the file exists but
there is an error parsing it. When run with `/bin/bash` it exits
0 in both cases as expected, but RPM scriptlets are run with sh.
To avoid this problem, we must always explicitly do an existence
check on the file before attempting to source it.
Signed-off-by: Adam Williamson <awilliam@redhat.com>