yang model revise: neutron-secgroups.yang

yang model revise: neutron-secgroups.yang

This patch revises yang model for security group and related codes.
- drop description for consistency which isn't very useful
- rename id to uuid for consistency
- drop backpointer. list of security rules in security group
  If openstack provider wants a list of rules associated to a given
  security group, walk through rules whose group is the uuid of the group
- eliminated the deprecated methods in neutron-spi

Change-Id: I7a3c79eae446858d6f0f4b8cd8757c85c1dab370
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Signed-off-by: Ritu Sood <ritu.sood@intel.com>