Fix usage of oslo.config

- make it possible to create a DBAPI instance given a config instance

- remove usage of global cfg.CONF instance (it's up to a user to pass
  a ConfigOpts instance to oslo.db)

- ensure end applications don't need to import/register/use config
  options directly - instead they pass a config instance to oslo.db
  helpers (EngineFacade.from_config() and DBAPI.from_config() class
  methods)

At the same time, usage of oslo.config remains completely optional as
we provide an API to pass those parameters programatically.

Change-Id: I1a00db7a4200ebdc96f17256ecbad430477e868f
replace string format arguments with function parameters

There are files containing string format arguments inside
logging messages. Using logging function parameters should
be preferred.

Change-Id: I089a4c51c0fe98906d74bcdbd5394e74631d0dba
Partial-Bug: #1321274
Merge "replace string format arguments with function parameters"
Merge "Fix usage of oslo.config"