PSA: autopkgtest amd64 workers

[Brian Murray]

The Ubuntu QA team has recently moved the majority of our amd64
autopkgtest test runners from one data center (lgw01) to another (lcy02).
A consequence of this move is that tests run on default instances, not in
big_packages, now have 4 GB of RAM and 2 vCPUs. While the instances for
packages in big_packages have the same amount of RAM and vCPUs but
slightly larger disks.

When looking at test logs there are two "tells" that they ran in the new
datacenter - lcy02 appearing in the `--security-groups` argument and
builder appearing in the `--flavor` argument.

If you happen to see anything odd in the autopkgtest logs for your
favorite packages please let us know!

Cheers,
--
Brian Murray