Port os-console-output extension to API v3 Part 2

This change includes:
    - changes to os-console-output fit into api-v3
    - unit test refactor to decrease code duplication
    - change the action name to get_console_output since it is more 'compliant
with all other servers actions, using '_' to separate the words in the
request.

Partially implements blueprint nova-v3-api

Change-Id: I075c868c3a160f06980edcc27ff22da910ff4403
Merge "Port os-console-output extension to API v3 Part 2"