Allow changes into gate with +2 from jenkins

If a change ends up with a +2 from jenkins but no approval (because
a core reviewer removed his or her vote), allow it to be enqueued
the next time someone approves it.

Change-Id: I0d21921ac6bfbf93fb136bba8e921f2257f57567
Merge "Allow changes into gate with +2 from jenkins"