Add check for a valid CQ-DEPEND field.

Common errors I've seen in the past:
  CQ-DEPENDS=1234
  CQ-DEPEND:1234

This CL catches all of the above plus more.

BUG=chromium:206541
CQ-DEPEND=CL:47271
TEST=Test with valid and invalid CQ-DEPEND fields.

Change-Id: Iafa4cb351d8f870289d72b09542218321ee6fa3c
Reviewed-on: https://gerrit.chromium.org/gerrit/47239
Tested-by: David James <davidjames@chromium.org>
Reviewed-by: Ryan Cui <rcui@chromium.org>
Commit-Queue: David James <davidjames@chromium.org>
2 files changed