Bug 4550 - always rebuild security group rule in security group

Bug 4550 - always rebuild security group rule in security group

The change set of 906836c289a7e4c3d33669d90515d77e75cfb6d,
the effort transparent neutron northbound api, caused not to update
security group rule in security group.
So always rebuild rules in NeutronSecurityGroup and keep
security group rule in security group of yang model empty list.

openstack service provider that uses MD-SAL should not use
security group rules in security rule. But it should listen to
data change notification on security group rules.

Change-Id: I7da2e23d9c45549d2f5d138dfea148e36bd8061b
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>