Run tests in individual sandbox

[Steap2448]

What has been done? Why? What problem is being solved?

I didn't forget about

• Tests
• Changelog
• Documentation

Close #122

[Totktonada]

If you plan to going toward the 'clean tarantool state from inside tarantool' direction, I suggest to pay attention to our attempts to solve problems of the same kind in test-run:

• pretest_clean.lua script.
• Issues around the script.

However I'll warn: this is almost infinite road and the implementation always will be flawed.

The reliable way is to actually run a separate tarantool instance. This, OTOH, leads to its own subtle differences (another working directory at least).

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I would think about usablity. Should the option be a user choise (command line option), a project wide configuration value (stored within the repository), a file/group/test scope configuration value? I don't know an answer, just highlighted that we should pay attention to this.