Remove _disassociate_floating_ip & _create_network

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

Replaced methods:
	* _disassociate_floating_ip (not used)
	* _create_network

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: I083d713c638de50b1549b4c10b9eb38f58b85fab
2 files changed