Resolve "Data Race in Change State Manager"

Change State Manager seems to produce a volatile data race.

Related Issue

Closes #131 (closed)

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.

api/initialise_test.go

@@ -5,6 +5,7 @@ import (
 	"net"
 	"os"
 	"testing"
+	"time"
 
 	cpb "code.fbi.h-da.de/cocsn/api/go/gosdn/core"
 	ppb "code.fbi.h-da.de/cocsn/api/go/gosdn/pnd"
@@ -71,13 +72,17 @@ func bootstrapUnitTest() {
 		log.Fatal(err)
 	}
 
+	mockChange := &mocks.Change{}
+	mockChange.On("Age").Return(time.Hour)
+	mockChange.On("State").Return(ppb.Change_INCONSISTENT)
+
 	mockPnd := mocks.NetworkDomain{}
 	mockPnd.On("ID").Return(pndUUID)
 	mockPnd.On("GetName").Return("test")
 	mockPnd.On("GetDescription").Return("test")
 	mockPnd.On("PendingChanges").Return([]uuid.UUID{changeUUID})
 	mockPnd.On("CommittedChanges").Return([]uuid.UUID{changeUUID})
-	mockPnd.On("GetChange", mock.Anything).Return(&nucleus.Change{}, nil)
+	mockPnd.On("GetChange", mock.Anything).Return(mockChange, nil)
 	mockPnd.On("AddDevice", mock.Anything, mock.Anything, mock.Anything).Return(nil)
 	mockPnd.On("GetDevice", mock.Anything).Return(&nucleus.CommonDevice{
 		UUID:     deviceUUID,