test: skip test-process-config if no config.gypi

If you run the tests in a different machine to the one you built on,
this test will fail. Avoid this by skipping if the file doesn't exist.
We shouldn't need to check that the file exists in this test, as the
build won't pass without a config.gypi anyway.

Also adds console.logs, so you can see what the actual difference
between the objects was, as `assert.deepStrictEqual()` only shows you
the first three lines.

PR-URL: https://github.com/nodejs/node/pull/16436


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>