Handle SIGINT on windows

[sdstolworthy]

See #254 (comment)
and #254 (comment)

Our test runner uses taskkill to interrupt the Sandbox watcher. This kills the node process without allowing the event queue to drain, leaving unresolved promises. In Sandbox, this is manifested by the post-deployment sandbox events not finishing before the process is killed. This causes tests to fail which rely on the presence of the client configuration generated in the after deployment event handler.

Right now, this is naively addressed by hardcoding a wait time in the code. This should be refactored to allow a more flexible approach. Either our Process interactor should be able to send "wait" interactions, or we should find a more elegant way to kill the process on windows.