#714 Update unit test generation scripts to pass custom import statements

[Kor de Jong]

The same unit tests will be used by the current pcraster_python module and the new multicore module. The only difference will be the import statements at the top of the test scripts:

from pcraster import *

or

from pcraster import *
from pcraster.multicore import *

These statements must be configurable upon unit test module generation.

[Kor de Jong]

This task requires that the pcraster_python unit tests run at all. At the moment they don't. See https://github.com/pcraster/pcraster/issues/6