pre-upload.py: enforce cq-depend/change-id positions

The CQ rejects CLs that have Cq-Depend's in places other
than the same paragraph as Change-Id, as shown in this
rejection message:

Your CL may be incorrectly using CQ feature(s):
 * Line 19: u'Cq-Depend: chromium:1626803, chromium:1626804,
 chromium:1626805, chromium:1626806, chromium:1620554, chromium:1627304,
 chromium:1627305': CQ-Depend must be in the last paragraph (like
 Change-Id:)

so checking it earlier can save one roundtrip.

BUG=none
TEST=tested both correct and incorrect input

Change-Id: I679785db2a62c0d1acbbf93239049588c6ae8921
Reviewed-on: https://chromium-review.googlesource.com/1639368
Commit-Ready: Luigi Semenzato <semenzato@chromium.org>
Tested-by: Luigi Semenzato <semenzato@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
2 files changed