arista-veos: first try to use in a lab

As for Juniper Firefly, the provisioning is done through TFTP. This
triggers an additional reboot. Maybe we can just add the image directly
instead?
arista-veos: just put the initial configuration in the image disk

This allows us to remove the DHCP/TFTP stuff which is quite interesting
but since vEOS has to reboot, it seems faster to do that this way. We
can still get the previous method by looking at the previous commit.
arista-veos: WIP: MLAG setup

The Mlag daemon is crashing. It seems to misinterpret something as a
local MAC address...
arista-veos: don't use locally administered MAC

Arista's MLAG implementation do not like them. Mlag daemon is choking on
it.
arista-veos: WIP: MLAG setup

Still doesn't work as expected. It seems that everything related to VLAN
3 is going through peer link. Also, OSPF doesn't seem to work...