test: use fs rimraf to refresh tmpdir

[cjihrig]

Ignore the first two commits, which are just #29168.

Commit: test: use fs rimraf to refresh tmpdir

If rimraf lands in core, we should use it to refresh the tmpdir in our test suite. We should be able to remove even more of this code (like spawning a child process), but I figured this was a good starting point.

Checklist

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

[gengjiawen]

https://travis-ci.com/nodejs/node/jobs/226852561#L270

=== release test-fs-readdir-ucs2 ===
Path: parallel/test-fs-readdir-ucs2
--- stderr ---
Can't clean tmpdir: /home/travis/build/nodejs/node/test/.tmp.602
Files blocking: [ '=�\u0004�' ]
/home/travis/build/nodejs/node/test/common/tmpdir.js:88
    throw e;
    ^
Error: Unable to rimraf /home/travis/build/nodejs/node/test/.tmp.602
    at rimrafSync (/home/travis/build/nodejs/node/test/common/tmpdir.js:42:11)
    at process.onexit (/home/travis/build/nodejs/node/test/common/tmpdir.js:73:5)
    at process.emit (events.js:214:15)
Command: out/Release/node /home/travis/build/nodejs/node/test/parallel/test-fs-readdir-ucs2.js