Add standard constants for CPU architectures

Introduce a nova/compute/arch.py module to serve a similar role
to nova/compute/vmmode.py, by providing constants for known
CPU architectures and validation/canonicalization APIs

Related-bug: #1348624
Change-Id: Idd4907b5488dd0832c15783d87d57d77ae654519
Add API schema for v2.1/v3 config_drive extension

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 v3-api-schema

Change-Id: Ia0681941c5449051c90425348466bd7dc44c2e45
Standardize logging for v2 api extensions

- add log translation hints for warning, error and info levels
- remove pointless debug message

Change-Id: I67c5e77e62f8ef89204b67426b88856ef91dfc26
Merge "Add API schema for v2.1/v3 config_drive extension"
Merge "Add standard constants for CPU architectures"
Merge "Standardize logging for v2 api extensions"