Log as ERROR only for conditions requiring operator attention

There is a tempest blueprint (https://blueprints.launchpad.net/tempest/+spec/fail-gate-on-log-errors) that proposes to start failing gate jobs if ERROR appears in the logs unexpectedly. There is a whitelist so that expected error conditions for a given project don't trigger failure, but at present Neutron logs so many things as ERROR that whitelisting is not feasible. A cleanup effort is required to reduce the incidence of logging as ERROR to cases that would conceivably require operator attention. Ideally the number of such conditions would be small enough that whitelisting wouldn't mask actual problems.

Tempest is going to start outputting all ERROR log lines in the gate jobs for Neutron so we can start eliminating the unnecessary logging to the point where whitelisting is possible. Once we're satisfied with the whitelisting, Tempest can start failing jobs that produce errors that aren't whitelisted.