e2e: Check number of output files

[odeimaiz]

What do these changes do?

Puppeteer checks number of output files produced by a node.

So far we were only checking if some output was produced. Now we can check a specific number of outputs.

P.S. Since the node's logs file was hiding the lack of other outputs, this PR will make master red again.

Related issue number

closes #1341

[codecov]

Codecov Report

Merging #1343 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1343      +/-   ##
==========================================
- Coverage   72.73%   72.65%   -0.09%     
==========================================
  Files         201      201              
  Lines        8356     8356              
  Branches      938      938              
==========================================
- Hits         6078     6071       -7     
- Misses       2005     2012       +7     
  Partials      273      273

Flag	Coverage Δ
#integrationtests	57.63% <ø> (-0.21%)	⬇️
#unittests	67.07% <ø> (+0.01%)	⬆️

Impacted Files	Coverage Δ
...erver/src/simcore_service_webserver/storage_api.py	35.29% <0%> (-23.53%)	⬇️
...rc/simcore_service_director/registry_cache_task.py	97.43% <0%> (+2.56%)	⬆️

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