STORAGEMODEL-299 fixing AttributeError

Traceback (most recent call last):
  File "C:\Jenkins\workspace\storagemodel\src\infi\storagemodel\examples\tests.py", line 15, in test_devlist_runs
    devlist()
  Local variables:
    'devlist': <function devlist at 0x0000000002CDABA8>
    'self': <infi.storagemodel.examples.tests.ExamplesTestCase testMethod=test_devlist_runs>
  File "C:\Jenkins\workspace\storagemodel\src\infi\storagemodel\examples\__init__.py", line 12, in devlist
    non_mp_devices = model.get_native_multipath().filter_non_multipath_scsi_block_devices(scsi_block_devices)
  Local variables:
    'get_storage_model': <function get_storage_model at 0x0000000002C80358>
    'mp_devices': []
    'scsi_block_devices': [<SCSIBlockDevice: \\?\GLOBALROOT\Device\0000004b for <SCSIDevice \\?\GLOBALROOT\Device\0000004b for PHYSICALDRIVE0 (<unknown-scsi-serial-number>)>>]
    'model': <infi.storagemodel.windows.WindowsStorageModel object at 0x00000000031BA0F0>
    'infinibox_vid_pid': ('NFINIDAT', 'InfiniBox')
  File "C:\Jenkins\workspace\storagemodel\src\infi\storagemodel\windows\native_multipath.py", line 60, in filter_non_multipath_scsi_block_devices
    return filter(lambda device: not is_disk_drive_managed_by_windows_mpio(device), scsi_block_devices)
  Local variables:
    'scsi_block_devices': [<SCSIBlockDevice: \\?\GLOBALROOT\Device\0000004b for <SCSIDevice \\?\GLOBALROOT\Device\0000004b for PHYSICALDRIVE0 (<unknown-scsi-serial-number>)>>]
    'self': <infi.storagemodel.windows.native_multipath.WindowsNativeMultipathModel object at 0x0000000003270F98>
  File "C:\Jenkins\workspace\storagemodel\src\infi\storagemodel\windows\native_multipath.py", line 60, in <lambda>
    return filter(lambda device: not is_disk_drive_managed_by_windows_mpio(device), scsi_block_devices)
  Local variables:
    'device': <SCSIBlockDevice: \\?\GLOBALROOT\Device\0000004b for <SCSIDevice \\?\GLOBALROOT\Device\0000004b for PHYSICALDRIVE0 (<unknown-scsi-serial-number>)>>
  File "C:\Jenkins\workspace\storagemodel\src\infi\storagemodel\windows\device_helpers.py", line 9, in is_disk_drive_managed_by_windows_mpio
    return disk_drive.parent._instance_id.lower() == MPIO_BUS_DRIVER_INSTANCE_ID
  Local variables:
    'disk_drive': <SCSIBlockDevice: \\?\GLOBALROOT\Device\0000004b for <SCSIDevice \\?\GLOBALROOT\Device\0000004b for PHYSICALDRIVE0 (<unknown-scsi-serial-number>)>>
AttributeError: 'WindowsSCSIBlockDevice' object has no attribute 'parent'