packaging: setup: keeping NFS ports open in case of preexisting exports

Looking for preexisting NFS exports in order to correctly evaluate
how to configure NFS related rules on the firewall.

Change-Id: Id99ac88af780c6239655676b5290230076d0284b
Bug-Url: https://bugzilla.redhat.com/1109326
Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>
(cherry picked from commit ad949fcf34a99885186db30b435675d595f546c9)