BZ #1130304 - nfs-utils should be installed before using nfs

https://bugzilla.redhat.com/show_bug.cgi?id=1130304

Make sure nfs-utils is installed and the selinux bit flipped (if
applicable) before attempting to nfs mount something in glance or
cinder.
`cinder::volume::nfs` calls `cinder::backend::nfs`, so this is ok :+1: