API schema for v3 console_output 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: Id6330e2250448c54679df4f27af25c2614a871f0
Merge "API schema for v3 console_output API"