packaging: setup: cleanup nfs exports usage

1. if exports.d exists and we registered ourselves previously in
   exports, move the entry to our own file.

2. if ACL specified enforce a new entry.

3. do not touch anything on upgrade unless (2).

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1058018
Change-Id: Ie3df61b1b52aead5ddf457da14f26324dbc2a56c
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>