[testlib] Fix test library docs and rearrange the Jupyter tests

[vkarak]

No description provided.

[codecov-commenter]

Codecov Report

Merging #2266 (8d171f1) into master (d1b89ac) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 8d171f1 differs from pull request most recent head bcec870. Consider uploading reports for the commit bcec870 to get more accurate results

@@            Coverage Diff             @@
##           master    #2266      +/-   ##
==========================================
- Coverage   86.12%   86.11%   -0.02%     
==========================================
  Files          56       56              
  Lines       10198    10190       -8     
==========================================
- Hits         8783     8775       -8     
  Misses       1415     1415              

Impacted Files	Coverage Δ
reframe/core/pipeline.py	92.75% <0.00%> (-0.09%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d1b89ac...bcec870. Read the comment docs.

[victorusu]

lgtm