pxeboot_stack container: use dhcplb for dynamic dhcp instead of dnsmasq

[pallotron]

The pxeboot_stack Docker container currently runs dnsmasq for DHCP, TFTP.
But the plan is to:

• replace dnsmasq DHCP with a personalised version of Meta's dhcplb.
• keep dnsmasq for TFTP and DNS
• keep nginx for webserver to serve:
  • initrd and vmlinuz (kernel) files
  • ipxe script to download the kernel and initrd from nginx
  • OS installer ramdisks
  • disk images
• Need to expose an gRPC API to provision/remove host reservations inside the dhcplb instance?
• The vm list command should get the private IP of the clients by talking to dhcplb?