[bugfix] Hide data-descriptors from variable attributes

[jjotero]

Closes #2000

[codecov-commenter]

Codecov Report

Merging #2047 (b575714) into master (7800833) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2047      +/-   ##
==========================================
+ Coverage   87.51%   87.53%   +0.02%     
==========================================
  Files          50       50              
  Lines        8874     8889      +15     
==========================================
+ Hits         7766     7781      +15     
  Misses       1108     1108              

Impacted Files	Coverage Δ
reframe/core/meta.py	98.96% <100.00%> (+0.06%)	⬆️
reframe/core/variables.py	96.09% <100.00%> (+0.03%)	⬆️

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[vkarak]

lgtm