post_gerrit_comment.sh: Add a helper to limit size of Gerrit comment

Trim the comment to be posted to be under 16K, which appears to be
Gerrit's limit (violating it causes error and build failure).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I645b84b5e6d931004f526a3463044af77151e7b5
2 files changed