Add missing unit test for segment db
Add missing unit test for segment db

This patch add test for get_dynamic_segment.

Change-Id: Icf676059a0dd24ad18b8632563c4de81190f0d04
Closes-Bug: #1684519

noironetworks/neutron,huntxu/neutron,eayunstack/neutron,openstack/neutron,mahak/neutron,openstack/neutron,huntxu/neutron,eayunstack/neutron,mahak/neutron,noironetworks/neutron,mahak/neutron,openstack/neutron