Add include dir for nitsi test

Add include dir for nitsi test

When we include recipes in our recipe we must be shure in some cases
that the recipe are generated out of a .in file.

All files in the include dir will be generated before every test so we
can be shure that these files are present.

This is useful for recipes like the make-install recipe in this test,
which needs to be generated and will be included in nearly every test.

Signed-off-by: Jonatan Schlag <jonatan.schlag@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>