gnt-dal cluster software setup

as per TPA-RFC-43, once the servers are shipped (#40966 (closed)) and burnt-in (#40969 (closed)), we need to work on the base setup.

• establish naming convention (gnt-dal? dal-node-XX?)
• confirm public IP allocation for the new Ganeti cluster
• establish reverse DNS delegation
• basic Debian install
  • dal-node-01
  • dal-node-02
  • dal-node-03
• mandos configuration (dal-node-01 done, needs to be tested)
• VLAN configuration
• establish private IP allocation for the backend network
• cross connects verification

this plan is slightly reworked from TPA-RFC-43 to take into account VLANs and the base Debian install, which were somehow omitted from the original proposal.

this might be split in one ticket per machine. next step once this is done is the ganeti setup (#40971 (closed)).