Better error handling

[odeimaiz]

What do these changes do?

• Error page:

  • Show human friendly error code text
  • More space for displaying entire error message

• Unresponsive backend:

  • Improve error handling
  • Add "Please, try again later" to 404 and 503 error messages

Related issue/s

closes #2283
closes #2350

How to test

Checklist

[codecov]

Codecov Report

Merging #2368 (44a7583) into master (c027086) will increase coverage by 0.0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master   #2368   +/-   ##
======================================
  Coverage    74.9%   74.9%           
======================================
  Files         513     513           
  Lines       20007   20007           
  Branches     1967    1967           
======================================
+ Hits        14998   14999    +1     
+ Misses       4494    4493    -1     
  Partials      515     515           

Flag	Coverage Δ
integrationtests	67.4% <ø> (ø)
unittests	68.4% <ø> (+<0.1%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ages/service-library/src/servicelib/aiopg_utils.py	87.5% <0.0%> (-3.2%)	⬇️
...ce_webserver/resource_manager/garbage_collector.py	74.0% <0.0%> (+0.8%)	⬆️
...webserver/computation_comp_tasks_listening_task.py	86.0% <0.0%> (+2.0%)	⬆️

[pcrespov]

🎉

[GitHK]

I see what you did here. It exposes a bit more of the underlying structure, but it works. Thanks a lot for this 👍

[sanderegg]

great addition!