Add the ability to force a disk reload on the widearea nodes even if the disk is up to date.
Add the ability to force a disk reload on the widearea nodes
even if the disk is up to date.

Add a sliceNN_alt_image pointer to a web location for downloading
a disk image in case the image isn't stored on the boot CD
(needed to handle heterogenous boot CD media)

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome