chore: moving file transfer tests to mender docker client

[merlin-northern]

Ticket: QA-1527

[mender-test-bot]

@merlin-northern, start a full integration test pipeline with:

• mentioning me and start integration pipeline

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[merlin-northern]

@mender-test-bot start integration pipeline you know what

[mender-test-bot]

Hello 😺 I created a pipeline for you here: Pipeline-2420650457

Build Configuration Matrix

Key	Value
INTEGRATION_REV	pull/2868/head
RUN_TESTS_FULL_INTEGRATION	true

[merlin-northern]

@danielskinstad the failure was unrelated, I restarted, and the automatic pipeline did run, but is not reported, due to some strange gitlab--github issue. those links are scrambled. I think this one was the one that will be reported here hopefully: https://gitlab.com/Northern.tech/Mender/integration/-/pipelines/2420648866 if not I will re-run. after restarting the github success stage it appeared.
Edit: you can ignore this comment, there was a bit of a hiccup with the pipelines but it is ok now