[bazel] //puppeteer-tests/util.ts: Shut down Puppeteer after tests finish.
[bazel] //puppeteer-tests/util.ts: Shut down Puppeteer after tests finish.

This prevents Puppeteer tests from hanging and timing out when running under Bazel.

Bug: skia:10614
Change-Id: I645b92f48d087c4e262557c1e40c0d1a0c37ca10
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/353696
Reviewed-by: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>
Commit-Queue: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>
Auto-Submit: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot