Investigate pull performance between native docker registries vs quay.io

[yuvipanda]

We recommend users put their custom docker images on quay.io. However, docker image pull performance affects new node spinup - especially important for dask clusters.

We should test have 15 nodes with SSD Base Disks come up at the same time, and try to pull the image. Knowing the difference in how long it takes here vs there will determine where we tell users to put their images. If it's an order of magnitude or so difference, we can suggest users put the image in their cloud registries.