Change the current gosdn plugin implementation from Go's internal plugin system to hashicorp's go-plugins

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

plugins/openconfig/cmd/main.go

 package main
 
 import (
+	"log"
+	"os"
+
 	"code.fbi.h-da.de/danet/gosdn/controller/plugin/shared"
-	"code.fbi.h-da.de/danet/gosdn/plugins/openconfig"
+	openconfig "code.fbi.h-da.de/danet/gosdn/plugins/openconfig"
 	"github.com/hashicorp/go-plugin"
 )
 
 func main() {
-	deviceModel, _ := openconfig.NewDeviceModel()
+	deviceModel, err := openconfig.NewDeviceModel()
+	if err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
 	plugin.Serve(&plugin.ServeConfig{
 		HandshakeConfig: shared.Handshake,
 		Plugins: map[string]plugin.Plugin{