Make _create_security_group() non-private

_create_security_group() is made public by this commit as
the tempest.scenario.manager interface is meant to be
consumed by tempest plugins.

Implements: blueprint tempest-scenario-manager-stable
Signed-off by: Soniya Vyas<svyas@redhat.com>

Change-Id: I6d862b4dd41ea86a659e6431bcb215e9e12cf35d
12 files changed