Specify database group instead of DEFAULT

At the request of Quantum folks, Let us switch from DEFAULT to
database for the database related options. This will help with
migration etc.

DocImpact

Fixes LP# 1171837

Change-Id: If602a6a7cc0f2a202632dd14574fea60dce4b589
Enable hacking H703: Multiple positional placeholders

Fix and enable test for multiple positional placeholders in
localizations

Change-Id: Ie3b5e3113cd0f3340b7b0f5774001893b1e6857c
Enable hacking H702 localization test

Fix and enable test for 'formatting operation should be outside of
localization method call'

Change-Id: I0e707f9d4aacf75f9a9239b323a57d7d39f30c84
Add generic serialization support

This adds a generic serialization model that the RpcProxy and
RpcDispatcher will use to serialize and deserialize arguments
and return values. The base definition is provided, as well
as a default NoOpSerializer which performs no special
action (retaining the existing behavior).

Related to blueprint rpc-object-serialization

Change-Id: I0a33baddee3e28dfc47100eb3216b679558b0bdd
Merge "Enable hacking H703: Multiple positional placeholders"
Merge "Enable hacking H702 localization test"
Merge "Specify database group instead of DEFAULT"