Add tests for execution modes

[rvhonorato]

There is currently support for 3 execution modes:

• batch: via HPCScheduler, a mode in which the application becomes a daemon directly interacting with the system's scheduler via system calls
• local: via Scheduler which uses the normal multiprocessing apis
• mpi: via MPIScheduler which is actually a pseudo-mpi implementation that works on stages; 1) the tasks are picked, 2) the run method of the MPIScheduler makes a system call with mpirun using a command-line interface 3) the haddock3-mpitask cli unpickes the tasks and 4) scatter the tasks using mpi4py api

Tests were added to cover the local execution but all other remain untested.

So tests needs to be added to the proper libraries and also integrations tests for each module running on each different execution modes are desireable