gen-tests.py improvements -- support for extra args
gen-tests.py improvements -- support for extra args

mbudiu-vmw/p4c-clone,p4lang/p4c,hanw/p4c,p4lang/p4c,p4lang/p4c,mbudiu-vmw/p4c-clone,mbudiu-vmw/p4c-clone,hanw/p4c,mbudiu-vmw/p4c-clone,p4lang/p4c,hanw/p4c,p4lang/p4c,hanw/p4c