Port security-group-default-rules extension into v2.1

This patch port security-group-default-rules into v2.1.

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: I4d65993d6413160d2c7c2eb2ce0c3f66768e1a36
Merge "Port security-group-default-rules extension into v2.1"