CBQE-2239: forkless interrupt watcher for win32

use mutiprocess module to create a child process
for running main testrunner in win32 while parent
watches for keyboard interrupts. unix machines
continue to use fork.

possible side-effect for win32 is inablity to enter pdb

Change-Id: Ia0ca7de1cc29f423efa7db6670d818bc5d085294
Reviewed-on: http://review.couchbase.org/36892
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>