[bgpvpn] Remove _get_server_port_id_and_ip4 & create_floating_ip

As tempest.scenario.manager was announced stable interface in Tempest
27.0.0[1] it can be now reused in plugins.

Replaced methods:
    * _get_server_port_id_and_ip4
    * create_floating_ip

Etherpad concerning this effort:
https://etherpad.opendev.org/p/tempest-scenario-manager-cleanup

[1] https://docs.openstack.org/releasenotes/tempest/v27.0.0.html#release-notes-27-0-0

Change-Id: I1490b2f9ab4972a6fcedc87868d5c444677d9096
1 file changed