test: simplify test skipping

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

test, doc

1. Make common.skip() exit. Also add common.printSkipMessage() for partial skips. Fixes: https://github.com/nodejs/node/issues/14016

2. Don't make needless things before skip

PR is big but seems easy to skim. Maybe it would be more convenient to review it commit by commit.