Adjust .mk files for parallel execution.
---------------------------- Test N1 ------------------------------
1:abc
2:def
---------------------------- Test N2 ------------------------------
1:abc
def
2:ghi
jkl---------------------------- Test N3 ------------------------------
2:def
3:
ghi
jkl---------------------------- Test N4 ------------------------------
2:ghi
jkl---------------------------- Test N5 ------------------------------
1:abc
2:def
3:ghi
4:jkl---------------------------- Test N6 ------------------------------
1:abc
2:def
3:ghi
4:jkl