As of 988243c93fb87190e1867ef913136ecf139e7cb8 in ipxe
"[virtio] Add virtio-net 1.0 support", VMs don't attempt
to boot over the network when using the virtio-net rom.
The ipxe-qemu package used in the grenade jobs contains
this problem. Switch to e1000 to avoid baremetal VMs
working on some hosts and not others.
Change-Id: I4ec297281380896ffe9004c4de7117586ded7149
Story: #2003808
Task: #26603
eabc48a901