Add support for subbosses to dhcpd_makeconf
Add support for subbosses to dhcpd_makeconf

Make sure we correctly handle subbosses by:
A) ignoring nodes which are assigned to other dhcp servers
B) correctly specifying the next-server and bootinfo options
   if boss is still the dhcp server and other subbosses are to
   handle those duties.

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