Make _cleanup_volume_type non-private

_cleanup_volume_type 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: Ia2116e9d1738276ae1edf566e6f5b9760d416ab9
1 file changed