Since there are three volume driver files relating to
Fujitsu ETERNUS DX in cinder.volume.drivers.fujitsu,
Due to the need to distinguish from the new series,
I make 'eternus_dx' directory at cinder.volume.drivers.fujitsu
and I move these files to the directory.
Change-Id: I605698e7cf028e4fcf4896ce676250b00ecb7c86