VOL-2868 Model simplification/removal.

Reduced the model to its most commonly used functions. (Removed unused logic & test cases.)
Reworked remaining functions to be more intuitive to use, and to more closely follow golang conventions.

Change-Id: Ibbb267ff37e039b73489b4379aa2654208614d5b
diff --git a/rw_core/core/logical_device_agent_test.go b/rw_core/core/logical_device_agent_test.go
index 0babfad..175fe06 100644
--- a/rw_core/core/logical_device_agent_test.go
+++ b/rw_core/core/logical_device_agent_test.go
@@ -487,9 +487,8 @@
 	clonedLD.DatapathId = rand.Uint64()
 	lDeviceAgent := newLogicalDeviceAgent(clonedLD.Id, clonedLD.Id, clonedLD.RootDeviceId, lDeviceMgr, deviceMgr, lDeviceMgr.clusterDataProxy, lDeviceMgr.defaultTimeout)
 	lDeviceAgent.logicalDevice = clonedLD
-	added, err := lDeviceAgent.clusterDataProxy.AddWithID(context.Background(), "/logical_devices", clonedLD.Id, clonedLD, "")
+	err := lDeviceAgent.clusterDataProxy.AddWithID(context.Background(), "logical_devices", clonedLD.Id, clonedLD)
 	assert.Nil(t, err)
-	assert.NotNil(t, added)
 	lDeviceMgr.addLogicalDeviceAgentToMap(lDeviceAgent)
 	return lDeviceAgent
 }