Apply suggestions from code review

Author: DaanHoogland

plugins/hypervisors/kvm/src/test/java/com/cloud/hypervisor/kvm/resource/wrapper/LibvirtRestoreBackupCommandWrapperTest.java

@@ -508,6 +508,7 @@ public void testExecuteWithMultipleVolumes() throws Exception {
                 "/var/lib/libvirt/images/volume-123",
                 "/var/lib/libvirt/images/volume-456"
         ));
+        when(command.getBackupFiles()).thenReturn(Arrays.asList("volume-123", "volume-456"));
         when(command.getBackupVolumesUUIDs()).thenReturn(Arrays.asList("volume-123", "volume-456"));
         when(command.getMountTimeout()).thenReturn(30);