Since the Moonshot cluster will soon have x86 nodes and those nodes do
call bootinfo (unlike the ARM nodes), make sure that bootinfo does not
send PXEBOOTING/BOOTING events (since dhcpd already has) by starting it
with the new -E option.
Formalize by adding a BOOTINFO_EVENTS defs var that defaults to 1.
This ensures that a nobootinfo version of the dhcpd.conf template is
installed and that bootinfo is invoked with the -E option.
Only defs-cloudlab-utah should set it to zero.