use `-c` to launch ipengine/ipcontroller on Windows Python 2

The previous behavior, introduced to workaround multiprocessing bugs (#4911),
caused an instance check failure, preventing `bind_kernel`
from being able to tell if the kernel is an engine.
Merge pull request #7202 from minrk/parallel-engine-main

use `-c` to launch ipengine/ipcontroller on Windows Python 2