Fix wrong migrations and fix tests in nova_notifier

This is a joint commit of 2 other commits from master:

For Postgres migrations are failed.
More then we can get for mysql an error
"Specified key was too long; max key length is 1000 bytes" in b6ae66d05e3
migration in some versions of dialect.
Fixes-Bug: #1219776
(cherry-picked from aae3f55304ff161b401b803769350e9cb66b0e8c)

The prototype for instance_update_and_get_original changed, so let's
ignore it completely for the future.
Fixes-Bug: #1221173
(cherry-picked from d2a87a9dfd3cd9ef034eed3d693683972c842576)

Change-Id: Id4d349bbc49cdc957076b3e211f70db9838cd4cb