test,win: cleanup exec-timeout processes

When CMD is used to launch a process and CMD is killed too quickly,
the process can stay behind running in suspended state, never
completing. This only happens in Windows Server 2008R2.

Refs: https://github.com/nodejs/build/issues/1829

PR-URL: https://github.com/nodejs/node/pull/28723


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Beth Griggs <Bethany.Griggs@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>