In Port Forwarding functional tests, port is created in setUp()
method. This port had specified exactly IP address and subnet to use.
This was proposed in [1] to fix issue when new port created in same
subnet got sometimes IP address outside of subnet range.
Unfortunatelly that fix was not enough and caused other issues
as sometimes this "fixed" IP address used for port might be
used e.g. by router_interface port and that caused sometimes
"409 conflict" response from Neutron sometimes.
This patch adds additional method in
neutron.tests.unit.db.test_db_base_plugin_v2 module to find first
free IP address from given subnet.
This method is now used in port forwarding tests module to choose
IP address for second created port in the subnet so there should be
no conflicts with IP addresses anymore.
[1] https://review.openstack.org/#/c/631815
Change-Id: Iee2f72acf6814a0f8f76d240862429a8b63c3b09
Closes-bug: #1813540
414bdd4c59