Remove _create_security_group & _create_empty_security_group

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

Replaced methods:
	* _create_security_group
	* _create_empty_security_group

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: I9b3245be474c3e23622de8e80e391247f2cf866f
2 files changed