test: refactor test-vm-new-script-new-context

* block scope test cases
* clean up global leaks in individual test cases
* enable global variable leak checking
* remove console.error() statements

PR-URL: https://github.com/nodejs/node/pull/14536


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>