Add an explicit ENTRYPOINT to the Agent "all" containers

[webbnh]

The Agent commands require the environment which the agent/profile script sets up. This script is normally run automatically when a user logs in by virtue of a symbolic link in /etc/profile.d; however, when a user invokes containerized Agent commands, although the profile script exists inside the container, there is no login performed, and so the script isn't run...and it is cumbersome to cause it to run inside the container environment in conjunction with running a pbench command (the easiest approach is to create a script (see contrib/containerized-pbench/README.md), but the user has to map that into the container in order to use it; otherwise, the user has to run an interactive shell inside the container, which is not much better).

This change provides a little script which source's the Agent profile script and then exec's the requested command inside the container, and makes use of it as the default entrypoint for the Agent "all" containers. This enables users to use a command line something like

$ podman run <cid> pbench-results-push

This PR makes the following changes:

• Adds a utility script for use as the containers entrypoint.
• Modifies the Agent container build to specify the new script as the container entrypoint if the container "type" is "all".

This PR also includes two new files in contrib/containerized-pbench:

• a pbench command script which wraps the container invocation and provides some helpful defaults; and,
• a "demo" script which shows how a user might run a benchmark using the containerized Agent commands.

These last two files don't need to be merged into the repo -- they are mostly provided as "functional documentation" showing how this change is useful. However, they do make it easy to run Agent commands, and they work without having to install the Agent.

[webbnh]

I think the wrinkles are all smoothed out and this PR is ready for review.

[dbutenhof]

Looks OK, even really nice, but simply looking at the files doesn't make it immediately obvious how to use them in combination. It'd be nice to update (or maybe even replace) contrib/containerized-pbench/README.md ...

And does the simpler example script ecosystem Pete set up in there still make sense? It'd be nice for the documentation to set some context.

[webbnh]

does the simpler example script ecosystem Pete set up in there still make sense?

This PR is very much an example of "run it up the flag pole and see who salutes".

I would like to see the agent/ changes merged into main. However, those changes alone are kind of abstruse without an explanation of how to use them, and using them repeatedly is easier with a wrapper script, so I added the pbench script, but I put it in contrib/, since it's not anything we plan on "shipping" at this point. And, then, rather than explaining how to use that script, it seemed easier and clearer to just provide a demonstration of it...hence the addition of the pbench_demo script in contrib/.

As far as I'm concerned, we don't need to merge the pbench_demo script (and, before we do, we should remove the definition of PB_AGENT_IMAGE_NAME, since, going forward, it shouldn't be pulling the image from this PR...), but we can merge it too if we like it as an example.

If people like the contrib/.../pbench script, etc., then I think we can remove the "example script ecosystem`, as what I'm submitting here should do all that in a more compact and accessible way...I think.

I can update the README.md if we decide to include either of the contrib/ files when this PR is merged.

[dbutenhof]

Well, I'd like to see this contrib stuff merged, because I think it makes the agent container workflow simpler, and this is something we all expect (are expected) to be doing over the next week. 😁

[webbnh]

this is something we all expect (are expected) to be doing over the next week.

My thoughts exactly. 😇 (This is why the demo_pbench script has that funky definition for PB_AGENT_IMAGE_NAME in it right now.... 😉)

[webbnh]

Converting to draft while I work the wrinkles out of the new approach.

[webbnh]

OK, I've reworked this change (and updated the PR): agent/profile is now untouched, and the container entrypoint is a new, little, wrapper script.

[webbnh]

OK, this is now ready to merge...if I could get one more round of approvals, please.