ch-fromhost in a Dockerfile

[qwofford]

It would be nice to have an option to ch-fromhost stuff in a Dockerfile. Since Dockerfile won't release an official syntax, maybe we could have a section like:

FROM yadda
RUN blah
FROMHOST nvidia

Not having this makes some things awkward. For example, on many-node jobs we need to run srun $SLURM_NODES ch-fromhost ... currently.

I want to be using squashfs images exclusively, and it's also not clear to me how we provision a squashfs container that doesn't yet have the proper injections.

[qwofford]

@pagrubel may want to track

[pagrubel]

@qwofford How does one track an issue automatically. Does the mention or my response do that?