Apply suggestions from code review

Author: DaanHoogland

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

@@ -71,6 +71,7 @@ public void testExecuteWithVmExistsNull() throws Exception {
         when(command.getRestoreVolumePools()).thenReturn(Arrays.asList(primaryDataStore));
         when(command.getRestoreVolumePaths()).thenReturn(Arrays.asList("/var/lib/libvirt/images/volume-123"));
         when(command.getBackupVolumesUUIDs()).thenReturn(Collections.singletonList("volume-123"));
+        when(command.getBackupFiles()).thenReturn(Arrays.asList("volume-123"));
         when(command.getVmState()).thenReturn(VirtualMachine.State.Running);
         when(command.getMountTimeout()).thenReturn(30);