[VOL-4178, VOL-3952] This commit removes flows/groups/meters persistency

This commit removes flows/groups/meters persistency from rw-core.
As part of this change, it also fixes a bug where devices were not
being loaded on an rw-core restart.  This is a necessary condition
to allow the non-persistency of flows/groups/meters to work.

This commit also renames "loader" to "cache" for the flows/groups/
meters to differentiate between data that is loaded from the KV
store and the one in cache.

Change-Id: Ib14e1450021abe30b17673c2910768fb740dba51
diff --git a/rw_core/core/device/agent_test.go b/rw_core/core/device/agent_test.go
index daf2508..88d901d 100755
--- a/rw_core/core/device/agent_test.go
+++ b/rw_core/core/device/agent_test.go
@@ -174,7 +174,7 @@
 	deviceMgr := dat.deviceMgr
 	clonedDevice := proto.Clone(dat.device).(*voltha.Device)
 	deviceAgent := newAgent(deviceMgr.adapterProxy, clonedDevice, deviceMgr, deviceMgr.dbPath, deviceMgr.dProxy, deviceMgr.defaultTimeout)
-	d, err := deviceAgent.start(context.TODO(), clonedDevice)
+	d, err := deviceAgent.start(context.TODO(), false, clonedDevice)
 	assert.Nil(t, err)
 	assert.NotNil(t, d)
 	for _, port := range dat.devicePorts {