[bugfix] Reset poll rate every time a test finishes the compilation or run phase

[ekouts]

One other thing we have talked about and would make sense to do in this PR is to expose SLEEP_MIN, SLEEP_MAX and SLEEP_INC_RATE in the configuration. It would be better to do it by partition but it would require more changes so maybe it's better to open an issue and do it in the next sprint. What do you think @vkarak ?

Fixes #2531.

[codecov-commenter]

Codecov Report

Merging #2534 (1971fdf) into master (e2d2406) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 1971fdf differs from pull request most recent head 0a38f66. Consider uploading reports for the commit 0a38f66 to get more accurate results

@@            Coverage Diff             @@
##           master    #2534      +/-   ##
==========================================
- Coverage   85.81%   85.80%   -0.01%     
==========================================
  Files          58       58              
  Lines       10800    10794       -6     
==========================================
- Hits         9268     9262       -6     
  Misses       1532     1532              

Impacted Files	Coverage Δ
reframe/frontend/executors/policies.py	92.28% <100.00%> (-0.14%)	⬇️

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[vkarak]

Still just a couple of minor changes.

[vkarak]

Lgtm now!

[vkarak]

I tested also with the example in #2531 and it seems to work correctly now.

[ekouts]

@jenkins-cscs retry all