Not sure how I got headed down this path, but here I am:
 * replace use of "ps" and "grep" with, wait for it..."pgrep"!
 * explicitly specify type=vif so we don't wind up with the extra,
   vifN.M-emu backend interface that gets left laying around,
 * add -F option to "xl shutdown" which is needed for HVMs else
   shutdown will fail and the domain won't go away (qemu left behind)
   and FBSD filesystem can be messed up,
 * Use "hd" instead of "sd" to avoid emulated SCSI driver which has
   caused me grief in the past (though it should never actually get
   used due to PVHVM config of kernel).