[bugfix] Document osext.cray_cdt_version() more precisely

[vkarak]

Fixes #1744.

[pep8speaks]

Hello @vkarak, 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 2021-02-18 16:58:38 UTC

[codecov-io]

Codecov Report

Merging #1796 (054ab35) into master (6b67d19) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1796   +/-   ##
=======================================
  Coverage   87.57%   87.57%           
=======================================
  Files          49       49           
  Lines        7919     7919           
=======================================
  Hits         6935     6935           
  Misses        984      984           

Impacted Files	Coverage Δ
reframe/utility/osext.py	84.71% <ø> (ø)

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