Update zfs.fedora init script

Apply all of Rudd-O's changes for the Fedora init script. The
initial init script was one I threw together based on Rudd-O's
original work. It worked for me but it has some flaws.

Rudd-O has invested considerable time updating it to be significantly
smarter. It now handles using ZFS as your root filesystem plus
various other quirks. Since he is familiar with the right
way to do things on Fedora and has tested this init script we
are integrating all of his changes.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>