[bgpvpn] Remove _create_port & create_keypair

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

Removed methods:
    * _create_port
    * create_keypair

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: Iec1b3d1d8655f20228cd98a49a39648c7bcf6a0a
2 files changed