VOL-2021 - default health check to true

also add nil check in case k8s closes before received is defined

Change-Id: Ic60d4ad005e79ff758a3fe09c0886a8398c2401b
diff --git a/ro_core/core/core.go b/ro_core/core/core.go
index cd27a42..8b0317b 100644
--- a/ro_core/core/core.go
+++ b/ro_core/core/core.go
@@ -86,11 +86,19 @@
 
 func (core *Core) Stop(ctx context.Context) {
 	log.Info("stopping-adaptercore")
-	core.exitChannel <- 1
+	if core.exitChannel != nil {
+		core.exitChannel <- 1
+	}
 	// Stop all the started services
-	core.grpcServer.Stop()
-	core.logicalDeviceMgr.stop(ctx)
-	core.deviceMgr.stop(ctx)
+	if core.grpcServer != nil {
+		core.grpcServer.Stop()
+	}
+	if core.logicalDeviceMgr != nil {
+		core.logicalDeviceMgr.stop(ctx)
+	}
+	if core.deviceMgr != nil {
+		core.deviceMgr.stop(ctx)
+	}
 	log.Info("adaptercore-stopped")
 }