[feat] Add convenience function to set a test variable only if it's undefined

[vkarak]

This PR adds a convenience function, set_var_default() to check if a variable is defined. to set a variable in a test only if it is not already defined. This is particularly useful in library tests, when you would like to set a default in a pipeline hook and you should only do that if the user has not defined another value with the -S option.

[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 2022-02-01 16:14:18 UTC

[vkarak]

Do you think that it would make sense to add also a set_var_default() convenience method? Users could write:

type(self).set_var_default('foo , 1)

instead of

if not type(self).is_var_defined('foo'):
    self.foo = 1

[vkarak]

Perhaps, we should better expose this functionality at the test level, so that users avoid the type(self) thing.

[codecov-commenter]

Codecov Report

Merging #2403 (2d2a80b) into master (5dc93df) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 2d2a80b differs from pull request most recent head ad68b98. Consider uploading reports for the commit ad68b98 to get more accurate results

@@           Coverage Diff           @@
##           master    #2403   +/-   ##
=======================================
  Coverage   85.63%   85.64%           
=======================================
  Files          56       56           
  Lines       10465    10471    +6     
=======================================
+ Hits         8962     8968    +6     
  Misses       1503     1503           

Impacted Files	Coverage Δ
reframe/core/meta.py	99.11% <ø> (ø)
reframe/core/pipeline.py	93.14% <100.00%> (+0.05%)	⬆️

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[vkarak]

I have hidden the metaclass stuff and I exposed a new function at the level of RegressionTest. Now users can simply do set_var_default('foo', 10) in their test.

[victorusu]

lgtm