For a new hostdev type='scsi_host' we have a number of
required functions for managing, adding, and removing the
host device to/from guests.  Provide the basic infrastructure
for these tasks.

The name "SCSIVHost" (and its variants) is chosen to avoid
conflicts with existing code named "SCSIHost" to refer to
a hostdev type='scsi' protcol='none'.
Signed-off-by: NEric Farman <farman@linux.vnet.ibm.com>