Convert camelCase attribute naming to camel_case

Convert cases of camelCase attribute naming to camel_case in the
security groups V3 API to make the v3 API as whole consistent in the naming
of attributes

Partially implements blueprint nova-v3-api

Change-Id: I3def0508d62194545a506ce845cfbfa2b87fd6f9
Merge "Convert camelCase attribute naming to camel_case"