Synchronize initramfs and system hostid

Synchronize initramfs and system hostid

Relying on an /etc/hostid file which is installed in the system
image breaks diskless systems which share an image.  Certain
cluster infrastructure such as MPI relies on all nodes having
a unique hostid.  However, we still must be careful to ensure
the hostid is syncronized between the initramfs and system
images when using zfs root filesystems.

To accompish this the automatically created /etc/hostid file has
been removed from the spl rpm packaging.  The /etc/hostid file
is now dynamically created for your initramfs as part of the
dracut install process.  This avoids the need to install it in
the actual system images.

This change also resolves the spl_hostid parameter handling
for dracut.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #398
Closes #399

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