fix(rest): detect session status from the pod state

[Alputer]

Closes reanahub/reana-ui#408

[codecov]

Codecov Report

Attention: Patch coverage is 16.66667% with 15 lines in your changes missing coverage. Please review.

Project coverage is 76.01%. Comparing base (4b0b2ff) to head (907459b).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
reana_workflow_controller/k8s.py	11.11%	8 Missing ⚠️
reana_workflow_controller/rest/workflows.py	22.22%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #611      +/-   ##
==========================================
- Coverage   76.59%   76.01%   -0.58%     
==========================================
  Files          17       17              
  Lines        1846     1864      +18     
==========================================
+ Hits         1414     1417       +3     
- Misses        432      447      +15     

Files with missing lines	Coverage Δ
reana_workflow_controller/rest/workflows.py	70.48% <22.22%> (-1.56%)	⬇️
reana_workflow_controller/k8s.py	79.31% <11.11%> (-4.52%)	⬇️

[tiborsimko]

Instead of "default" namespace value, we could use the one we have in r-commons, i.e. REANA_RUNTIME_KUBERNETES_NAMESPACE.

[tiborsimko]

Commit message cosmetics: instead of "get the session status from..." we could say "detect session status from..."

[tiborsimko]

Commit scope cosmetics: since the commit touches component named k8s.py or rest/workflows.py, we should rather use fix(rest) instead of fix(sessions). The scope is usually named after the component or the subcomponent of the source code that the commit touches; it is not named after the functionality. Although we have not been respecting this conventional commits semantics so for so strictly everywhere 😉