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.

controller/api/api_test.go

@@ -7,9 +7,7 @@ import (
 	"testing"
 
 	ppb "code.fbi.h-da.de/danet/gosdn/api/go/gosdn/pnd"
-	spb "code.fbi.h-da.de/danet/gosdn/api/go/gosdn/southbound"
 	tpb "code.fbi.h-da.de/danet/gosdn/api/go/gosdn/transport"
-	"code.fbi.h-da.de/danet/gosdn/controller/nucleus"
 	"code.fbi.h-da.de/danet/gosdn/controller/store"
 	log "github.com/sirupsen/logrus"
 	"github.com/spf13/viper"
@@ -32,7 +30,7 @@ func Test_GetIds(t *testing.T) {
 }
 
 func ensureFilesForTestsAreRemoved() {
-	ensureStoreFileForTestsIsRemoved(store.SbiFilenameSuffix)
+	ensureStoreFileForTestsIsRemoved(store.PluginFilenameSuffix)
 	ensureStoreFileForTestsIsRemoved(store.NetworkElementFilenameSuffix)
 }
 
@@ -59,11 +57,7 @@ func ensureStoreFileForTestsIsRemoved(storeName string) {
 func Test_AddPnd(t *testing.T) {
 	defer ensureFilesForTestsAreRemoved()
 
-	sbi, err := nucleus.NewSBI(spb.Type_TYPE_OPENCONFIG)
-	if err != nil {
-		t.Errorf("AddPnd() error = %v", err)
-	}
-	resp, err := AddPnd(context.TODO(), bufnet, "test", "test pnd", sbi.ID().String())
+	resp, err := AddPnd(context.TODO(), bufnet, "test", "test pnd")
 	if err != nil {
 		t.Error(err)
 		return