Add change abandoned logic to jeepyb

This change allows jeepyb to update LP bugs associated
to Gerrit changesets when those changesets
are abandoned.
Another change in openstack-infra/config will be needed
to configure review.openstack.org appropriately.

Partial-Bug: 1248813
Change-Id: I51ab97f240d161704fb323787fb54ee1814bd7fa
Merge "Add change abandoned logic to jeepyb"