Remove vol_get_usage_by_time from conductor api/rpcapi

In Havana, commit 3cf4cb253 moved the volume usage notify code to
conductor.

In Juno, commit 47f6ffad8 dropped vol_get_usage_by_time from conductor
manager but not from the conductor api/rpcapi modules. Without
vol_get_usage_by_time being in conductor manager it's an API pointing to
nothing and won't work so we should remove it.

The DB APIs are left in since the vol_usage_update DB API is tested
using vol_get_usage_by_time.

If we were to leave the conductor APIs in tree, we should add the
conductor manager method back in and convert the volume_usages table to
nova objects, and possibly also expose it via a v2.1 API extension.

Closes-Bug: #1434687

Change-Id: Ie2980d681c62cd3457b359fbe4f5c32a2bcfc5db

nova/conductor/api.py

@@ -108,9 +108,6 @@ class LocalAPI(object):
         return self._manager.block_device_mapping_get_all_by_instance(
             context, instance, legacy)
 
-    def vol_get_usage_by_time(self, context, start_time):
-        return self._manager.vol_get_usage_by_time(context, start_time)
-
     def vol_usage_update(self, context, vol_id, rd_req, rd_bytes, wr_req,
                          wr_bytes, instance, last_refreshed=None,
                          update_totals=False):

nova/conductor/rpcapi.py

@@ -137,6 +137,7 @@ class ConductorAPI(object):
            - Remove aggregate_host_add() and aggregate_host_delete()
            - Remove network_migrate_instance_start() and
              network_migrate_instance_finish()
+           - Remove vol_get_usage_by_time
 
     ... Icehouse supports message version 2.0.  So, any changes to
     existing methods in 2.x after that point should be done such
@@ -216,12 +217,6 @@ class ConductorAPI(object):
         return cctxt.call(context, 'block_device_mapping_get_all_by_instance',
                           instance=instance_p, legacy=legacy)
 
-    def vol_get_usage_by_time(self, context, start_time):
-        start_time_p = jsonutils.to_primitive(start_time)
-        cctxt = self.client.prepare()
-        return cctxt.call(context, 'vol_get_usage_by_time',
-                          start_time=start_time_p)
-
     def vol_usage_update(self, context, vol_id, rd_req, rd_bytes, wr_req,
                          wr_bytes, instance, last_refreshed=None,
                          update_totals=False):