Add API input validation framework

This patch adds a core part of API validation framework.
Other patches of each API schema are necessary.

The validation method is implemented with jsonschema library,
and some features are added:
 * validate minimum/maximum value of string number(ex. "10")
 * validate uuid string format

This framework can validate requests of both JSON and XML,
because of validating data after JSON/XML deserialization.

The API schema files for Nova v3 API will be created under
nova/api/openstack/compute/schemas/v3. For preparing these
files, this patch adds some __init__.py files.

blueprint nova-api-validation-fw

Change-Id: Ieba96718264ad2ddfba63b65425f7e5bbb8606a9
Merge "Add API input validation framework"