[@container] Move parsing support helpers to cq-testcommon.js
Functions were duplicated across test files.
Change-Id: I61d7d03fb57547e8f0b52bc4d27e1efc4504280d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5869120
Reviewed-by: Anders Hartvoll Ruud andruud@chromium.org
Commit-Queue: Rune Lillesveen futhark@chromium.org
Cr-Commit-Position: refs/heads/main@{#1356983}