test: fix assertion in vm test

Prototypes are not strict equal when they are from
different contexts. Therefore, assert.strictEqual()
fails for objects that are created in different
contexts, e.g., in vm.runInContext().

Instead of expecting the prototypes to be equal,
only check the properties of the objects
for equality.

PR-URL: https://github.com/nodejs/node/pull/11862


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>