Porting SecurityGroup related controller into v2.1

This patch port SecurityGroup, ServerSecurityGroup and SecurityGroupAction
controller into v2.1 security_groups extension.

This patch just move the v2 code into v2.1 and share the unittest. The other
v2.1 related fix and improvement will be addressed by subsequent patchset.

Partially implements blueprint v2-on-v3-api

Change-Id: I93951ce677b74ebed7db1b2fff1f788344806dba
Merge "Porting SecurityGroup related controller into v2.1"