Fix PostUploadHook for Gerrit issues

A gerrit change must contain the "Change-Id" at the end. This CL strips
out the changeId from the description and adds it back in at the end.

BUG=skia:5676
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2299303002
NOTRY=true

Review-Url: https://codereview.chromium.org/2299303002
1 file changed