Modified API calls in os usage

We usually call v3 keystoneclient APIs for V2 OSC, this patch
modified 'tenants' to 'projects'.

Change-Id: Idbf74f098cd1386aa675c081480b89bbc11c8534

Author: jiahui.qiang

openstackclient/compute/v2/usage.py

@@ -89,7 +89,7 @@ def _format_project(project):
         # Cache the project list
         project_cache = {}
         try:
-            for p in self.app.client_manager.identity.tenants.list():
+            for p in self.app.client_manager.identity.projects.list():
                 project_cache[p.id] = p
         except Exception:
             # Just forget it if there's any trouble