Add API schema for v3 agents API

By defining the API schema, it is possible to separate the validation
code from the API method. The API method can be more simple.
In addition, a response of API validation error can be consistent for
the whole Nova API.

Partially implements blueprint nova-api-validation-fw

Change-Id: Iae1bff0e853e1dc597ebdca07efeb477b105469e
Define common API parameter types

This patch defines some common API parameter types for API validation.
By sharing the parameter types between the whole Nova API, that would
make the APIs more consistent.

Partially implements blueprint nova-api-validation-fw

Change-Id: Ic1e25c8ccedbcefc5818f223049eaa3f9eb04959
Merge "Define common API parameter types"
Merge "Add API schema for v3 agents API"