[bugfix] Treat properly Slurm constraints with .

[Guy-Coates]

The reframe slurm node constraint validator rejects features with a "." in the name (eg nodes with Feature=c5.xlarge defined in slurm).

This results in Reframe generating no tests when attempting to target nodes of that type using --constraint=c5.xlarge in the systems.partitions.access config.

This PR relaxes the validation/tokenisation regexes to allow ".".

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.95%. Comparing base (94bae27) to head (8d86d40).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3667   +/-   ##
========================================
  Coverage    91.95%   91.95%           
========================================
  Files           62       62           
  Lines        13762    13762           
========================================
  Hits         12655    12655           
  Misses        1107     1107           

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[vkarak]

Thanks for the fix! Lgtm. Since we are not going to make another patch release for 4.9 (4.10 is around the corner), we'd need to rebase this PR on develop.

[vkarak]

Rebased PR on develop.