marine_test: change directory mapping between tests

[folex]

Currently, if a service writes some state to the disk by a static file name, this state is shared between different tests. This leads to 2 things:

1. Tests can't run in parallel because of an implicit shared state
2. Each test has to clean state on the disk (either in the beginning, or at the end, or even both)

This makes tests very fragile and cluttered: forget to clean state and you have a failing test that is really hard to debug.

I think the situation can be improved by generating directory mapping randomly. For example, /tmp can be mapped to /tmp/$UUID on the host.

[folex]

Here's an example of defensive state-cleaning in AquaDHT tests: https://github.com/fluencelabs/aqua-dht/blob/9a729611c6da4930b5f145696bfdc975d1227e77/service/src/tests.rs#L127