ovirt.te: add svirt avc for nfs

This patch adds the following avc:
  - allow svirt_t nfs_t:file open;

Change-Id: Ieeb3ea564c80b3a24ed643dcf6b352c40bd3a5b4
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>