[doc] Update documentation of built-ins and update tutorial examples removing the use of __init__

[jjotero]

• The documentation on the variable built-in was out of date. This section has now been updated to show its current capabilities.
• A sentence was added in the parameter built-in section indicating that the parameterized_test decorator will be deprecated.

The basic examples shown in the built-ins section are good enough to illustrate their capabilities, so there is no need to add another tutorial explaining these. Instead, a statement has been added in the introduction of the Writing reusable tests tutorial encouraging users to read the basic examples from the built-ins section of the ReFrame manual.

Closes #1935.

This also relates to #1899.

[ekouts]

lgtm in general, I had two very small comments while reading again the documentation

[pep8speaks]

Hello @jjotero, 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 2021-04-26 21:51:16 UTC

[codecov-commenter]

Codecov Report

Merging #1940 (54804a5) into master (45fbacb) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1940      +/-   ##
==========================================
- Coverage   87.90%   87.89%   -0.01%     
==========================================
  Files          50       50              
  Lines        8620     8627       +7     
==========================================
+ Hits         7577     7583       +6     
- Misses       1043     1044       +1     

Impacted Files	Coverage Δ
reframe/utility/__init__.py	92.82% <ø> (ø)
reframe/core/runtime.py	88.95% <0.00%> (-0.21%)	⬇️
reframe/frontend/cli.py	76.03% <0.00%> (+0.04%)	⬆️

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[jjotero]

@jenkins-cscs retry dom

[vkarak]

One additional thing we could do is to add note somewhere in the first tutorial saying that the classic way of setting up a test in its __init__() is still valid and not deprecated.

[vkarak]

I just found a minor typo. @teojgo Are you fine moving the sanity_patterns definition to the class body in the container_test?

[vkarak]

I was about to merge it, but the CI of the tutorials fails. I fixed a couple of typos, but @jjotero can you fix the rest?