test: skip irrelevant test on Windows

Skip test-cluster-disconnect-handles on Windows.

PR-URL: https://github.com/nodejs/node/pull/12261
Ref: https://github.com/nodejs/node/pull/12197#issuecomment-292228866


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>