[feat] Improve the container platform API exposed to tests

[teojgo]

• Respect the entrypoint and command defined inside the container image.
• Deprecate workdir and commands fields.
• Introduce the command field.
• Allow to skip pulling of the container image from a container registry.
• Expand container platform tutorial example.

Fixes #1736

• Need to change also the documentation
• Change the tutorial example
• Add a tutorial example for making files available outside of the container
• Deprecate the workdir and command fields

[teojgo]

@ChristianKniep please give your feedback

[kniec]

Sweat, just some minor comments. I reckon that the pull_command is a bandaid until a more sustainable way forward is found. Might be that skopeo is the ultimate swiss army knife for downloading and transforming image. @vrothberg
Valentin might also have an opinion about adding podman here... :)

[vrothberg]

Sweat, just some minor comments. I reckon that the pull_command is a bandaid until a more sustainable way forward is found. Might be that skopeo is the ultimate swiss army knife for downloading and transforming image. @vrothberg
Valentin might also have an opinion about adding podman here... :)

Thanks for pulling me in. Skopeo is super powerful and light weight. Podman, on the other hand, has Python bindings: https://github.com/containers/podman-py

[codecov-io]

Codecov Report

Merging #1775 (be72092) into master (35c3020) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1775      +/-   ##
==========================================
+ Coverage   87.60%   87.62%   +0.02%     
==========================================
  Files          49       49              
  Lines        7940     7954      +14     
==========================================
+ Hits         6956     6970      +14     
  Misses        984      984              

Impacted Files	Coverage Δ
reframe/core/containers.py	97.97% <100.00%> (+0.33%)	⬆️
reframe/core/pipeline.py	91.72% <100.00%> (ø)

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[pep8speaks]

Hello @teojgo, Thank you for updating!

Cheers! There are no PEP8 issues in this Pull Request!Do see the ReFrame Coding Style Guide

Comment last updated at 2021-03-04 13:54:17 UTC

[teojgo]

@kniec the PR is more or less ready. I have made various changed taking into account your comments. I have also expanded the tutorial for containers to include Sarus.

[kniec]

Thanks for the effort - I was busy this week, but I'll carve out some time in the next couple of days to go through it.