test: Implement logic to clear LocalGcs after each test

[pawelpasterz]

Fixes #1578

Change description:

• there are only 2 tests that require pre-uploaded files -- now they upload filed on their own (ArgsHelperTest#assertGcsFileExists succeeds & TestRunnerTest#mockedAndroidTestRun gcsAndHistoryName)
• Google API provides FakeStorageRpc which is created with LocalStorageHelper.getOptions()
• FakeStorageRpc can be cleaned/reseted only by calling LocalStorageHelper.getOptions() (both its hashmaps are cleared)
• Above is, unfortunately, the only way to clear FakeStorageRpc -- storage has reset method but it's not exposed
• The TestStorageProvider is introduced to wrap additional test logic
• Intention behind TestStorageProvider is GcStorage should not be aware of how it is used (tests or production )
• The TestStorageProvider has nullable Storage filed. It can be cleared (set null) with #clearStorage
• If storage is null TestStorageProvider will invoke LocalStorageHelper.getOptions() and assign reference to storage field.
• FlankTestRunner has a custom listener that will invoke LocalGcs#clear() after each test run

Test Plan

How do we know the code works?

Unfortunately, there is no straightforward way to verify it since OOM error occurred only on GH Actions machines, randomly.

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CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

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Timestamp: 2021-03-05 12:59:52
Buildscan url for ubuntu-workflow run 624465647
https://gradle.com/s/pdd6aycqraa2g

[pawelpasterz]

@flank-it

[github-actions]

Integration tests succeed for all OSes ✅
Windows Build scan:
MacOS Build scan:
Linux Build scan: https://gradle.com/s/xj3xcfn4375la
Workflow run https://github.com/Flank/flank/actions/runs/624381115