Slurm computation manager: improve unit test coverage

[sylvlecl]

• Do you want to request a feature or report a bug?

Quality improvement.

• What is the current behavior?

The slurm computation manager has integration tests, but the pure unit tests could cover a larger part of the code.

• What is the expected behavior?

We could increase the coverage on some parts:

• flag files monitor

• scontrol monitor

• general task management behaviour (cancels etc.)
  This will require to mock some inner used components (file system, command runner), and maybe to design another inner interface which would encapsulate closely the interactions with slurm.

• What is the motivation / use case for changing the behavior?

Robustness, and "auto-documentation".
For example, the flag files monitor behaviour could be illustrated with simple unit tests.

• Please tell us about your environment:
  • PowSyBl Version: ...
  • OS Version: ...