fix: Nested subdirectories in results-dir

[piotradamczyk5]

Fixes #1309

Nested directories are supported out of the box in GCloud results upload.
However Flank has an issue that it throws an exception because it did not properly store results in the local directory.
In order to support nested directories, local issue must be fixed

Test Plan

How do we know the code works?

1. Set configuration to contains nested result directories usimg results-dir
   ex:

gcloud:
...
  results-dir: nested/results
....

2. Run tests and see that results are properly updated to GCloud storage and stored locally

Checklist

• Unit tested

[github-actions]

Timestamp: 2020-11-16 16:10:15
Buildscan url for ubuntu-workflow run 366344257
https://gradle.com/s/jelrjpzitor72

[pawelpasterz]

Please, update the description with more explanatory Test Plan

[pawelpasterz]

I think it would be worth verifying if the subdirectories feature requires additional permissions. If it does, we could display a
suitable message

[piotradamczyk5]

Please, update the description with more explanatory Test Plan

done 👍

[piotradamczyk5]

I think it would be worth verifying if the subdirectories feature requires additional permissions. If it does, we could display a
suitable message

With current permissions, it works fine so I guess it does not need additional permission

[adamfilipow92]

• Tested, flank finish without exception
• Results uploaded properly
  👍