[sfc] Remove _get_router & _create_network

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

Removed methods:
    * _get_router
    * _create_network

There is a slight difference between tempest's get_router and this one.
Most changes are just fixes, without bigger logical interference.
See related patches below.[2][3]

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
[2] https://opendev.org/openstack/tempest/commit/3484f9901ca9c5c6607932d8dc4a7a451e817a59
[3] https://opendev.org/openstack/tempest/commit/0090a1048c0ad412e6c2f0bf0a0a91a393e09960

Change-Id: Ib185214a904333e597ac14e0501d942a93ab53f3
1 file changed