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
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 4652af4..99a3f32 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -486,7 +486,7 @@
             snapshot['id'])['snapshot']
         return snapshot
 
-    def _cleanup_volume_type(self, volume_type):
+    def cleanup_volume_type(self, volume_type):
         """Clean up a given volume type.
 
         Ensuring all volumes associated to a type are first removed before
@@ -542,7 +542,7 @@
         volume_type = volume_type_resp['volume_type']
 
         self.assertIn('id', volume_type)
-        self.addCleanup(self._cleanup_volume_type, volume_type)
+        self.addCleanup(self.cleanup_volume_type, volume_type)
         return volume_type
 
     def create_loginable_secgroup_rule(self, secgroup_id=None, rulesets=None):