Remove usage of local config object in Vitrage
services and tests. Instead, it's been replaced
with the global CONF object. The structure of the
code becomes more like in other OpenStack projects.
Also, this change provides an opportunity to
introduce migrations and tests for them.
Story: 2004059
Task: 27065
Change-Id: I37544a350adf8ca38a6fc4ff5d0fd96e38a3f922