Add simple DB checks for proper OS specification. Currently, just PCs are checked against the disk_images table. There is not dnard support and no create-os support.
Add simple DB checks for proper OS specification. Currently, just PCs
are checked against the disk_images table. There is not dnard support
and no create-os support.

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