Use --no-cache option in order to force re-scan of server ssh keys.

Currently we run ssh-keyscan to gather server keys for the ssh container. Since we typically want this to always run on a build, we may want to use the --no-cache build option.

requested review from @s-anelso56

Yeah, this is a good catch. I thought Docker didn't cache intermediates for RUN commands, but it obviously is here. Feel free to merge this up.

I'm merging develop up to add a new VM to the SSH keyscan list. Since this looks good, I'll merge it with the rest.

mentioned in commit 58fc3ef7

merged