[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/logical_agent_meter_helpers.go b/rw_core/core/device/logical_agent_meter_helpers.go
index 8bffba9..654392e 100644
--- a/rw_core/core/device/logical_agent_meter_helpers.go
+++ b/rw_core/core/device/logical_agent_meter_helpers.go
@@ -32,7 +32,7 @@
 		if flowMeterID := fu.GetMeterIdFromFlow(flow); flowMeterID != 0 {
 			if _, have := metersConfig[flowMeterID]; !have {
 				// Meter is present in the flow, Get from logical device
-				meterHandle, have := agent.meterLoader.Lock(flowMeterID)
+				meterHandle, have := agent.meterCache.Lock(flowMeterID)
 				if !have {
 					logger.Errorw(ctx, "Meter-referred-by-flow-is-not-found-in-logicaldevice",
 						log.Fields{"meterID": flowMeterID, "Available-meters": metersConfig, "flow": *flow})
@@ -65,7 +65,7 @@
 		return true
 	}
 
-	meterHandle, have := agent.meterLoader.Lock(meterID)
+	meterHandle, have := agent.meterCache.Lock(meterID)
 	if !have {
 		logger.Debugw(ctx, "Meter-is-not-present-in-logical-device", log.Fields{"meterID": meterID})
 		return true