Fix seg-fault issues when initializing NEST

[med-ayssar]

fixes #3400

[med-ayssar]

@heplesser, in testsuite/do_tests, I just removed the line with mpi command that was added to avoid the seg-fault, other changes are made with my editor formatter (spaces and tabs stuff)

[heplesser]

@med-ayssar Thanks for your PR! I am not really happy with the formatting changes to do_tests.sh. Would you mind if I ported your changes to pynestkernel_api.pyx manually? I will credit you as co-author! And I will check with the original authors of the file about the two initialization functions.

[med-ayssar]

Yeah, I don't mind. If you want, I can even revert the changes in the do_tests file.

[heplesser]

@med-ayssar Great if you could revert!

[med-ayssar]

@heplesser, reverted!

[heplesser]

Thanks!