Unbreak elastic-recheck

A few bugs have crept into elastic-recheck causing it to fail. This
patch fixes them.

* an update to gerritlib broke FailedEvent.rev and change, since both of
  these should always be numbers cast to ints
* We appear to be missing files occasionally, add better logging for
  (also simplify Exception classes)
* Remove last usage of skip_resolved (removed in a previous patch)

Change-Id: Ifc180989832be152e08a4873e62857a899835484