fix(k8s): handle exceptions when creating dask cluster

[Alputer]

Closes #617

[codecov]

Codecov Report

Attention: Patch coverage is 24.56140% with 43 lines in your changes missing coverage. Please review.

Project coverage is 75.45%. Comparing base (7896c61) to head (0eecea0).

Files with missing lines	Patch %	Lines
reana_workflow_controller/dask.py	23.63%	42 Missing ⚠️
reana_workflow_controller/consumer.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #618      +/-   ##
==========================================
- Coverage   76.61%   75.45%   -1.16%     
==========================================
  Files          17       17              
  Lines        1847     1874      +27     
==========================================
- Hits         1415     1414       -1     
- Misses        432      460      +28     

Files with missing lines	Coverage Δ
reana_workflow_controller/k8s.py	88.88% <ø> (+5.06%)	⬆️
reana_workflow_controller/consumer.py	55.76% <50.00%> (+0.55%)	⬆️
reana_workflow_controller/dask.py	62.20% <23.63%> (-14.17%)	⬇️