[VOL-3117] Read KV store data path prefix from an environment variable

- voltha-lib-go reads the KVStoreDataPrefix from env variable, so removed the command-line flag in voltha-go
- also removed unused corepair topic flag
Change-Id: Ibe8403bf187126b587a92cd9c58aa6d923f84cd0
diff --git a/rw_core/core/device/agent_test.go b/rw_core/core/device/agent_test.go
index 29d8062..cd49681 100755
--- a/rw_core/core/device/agent_test.go
+++ b/rw_core/core/device/agent_test.go
@@ -112,7 +112,7 @@
 
 func (dat *DATest) startCore(inCompeteMode bool) {
 	cfg := config.NewRWCoreFlags()
-	cfg.CorePairTopic = "rw_core"
+	cfg.CoreTopic = "rw_core"
 	cfg.DefaultRequestTimeout = dat.defaultTimeout
 	cfg.KVStorePort = dat.kvClientPort
 	cfg.InCompetingMode = inCompeteMode
@@ -129,8 +129,7 @@
 		Host:                    cfg.KVStoreHost,
 		Port:                    cfg.KVStorePort,
 		Timeout:                 cfg.KVStoreTimeout,
-		LivenessChannelInterval: cfg.LiveProbeInterval / 2,
-		PathPrefix:              cfg.KVStoreDataPrefix}
+		LivenessChannelInterval: cfg.LiveProbeInterval / 2}
 	dat.kmp = kafka.NewInterContainerProxy(
 		kafka.InterContainerHost(cfg.KafkaAdapterHost),
 		kafka.InterContainerPort(cfg.KafkaAdapterPort),
@@ -142,13 +141,13 @@
 	proxy := model.NewDBPath(backend)
 	dat.adapterMgr = adapter.NewAdapterManager(proxy, dat.coreInstanceID, dat.kClient)
 
-	dat.deviceMgr, dat.logicalDeviceMgr = NewManagers(proxy, dat.adapterMgr, dat.kmp, endpointMgr, cfg.CorePairTopic, dat.coreInstanceID, cfg.DefaultCoreTimeout)
+	dat.deviceMgr, dat.logicalDeviceMgr = NewManagers(proxy, dat.adapterMgr, dat.kmp, endpointMgr, cfg.CoreTopic, dat.coreInstanceID, cfg.DefaultCoreTimeout)
 	dat.adapterMgr.Start(context.Background())
 	if err = dat.kmp.Start(); err != nil {
 		logger.Fatal("Cannot start InterContainerProxy")
 	}
 
-	if err := dat.kmp.SubscribeWithDefaultRequestHandler(kafka.Topic{Name: cfg.CorePairTopic}, kafka.OffsetNewest); err != nil {
+	if err := dat.kmp.SubscribeWithDefaultRequestHandler(kafka.Topic{Name: cfg.CoreTopic}, kafka.OffsetNewest); err != nil {
 		logger.Fatalf("Cannot add default request handler: %s", err)
 	}