The following change makes the check for the nbd port or named export
more robust.
I wasn't sure whether to include sed in the dracut_install() of
module-setup.sh since net already does that (and nbd depends on that).
Name based connects fail because of the quotes around the $nbdport.
For name based connects, the -N option also gets included. For
instance nbd-client 192.168.0.1 '-N ltsp' /dev/nbd0.
I believe the quotes are not necessary for actual port numbers.