File tests.unit.volume.v2.fakes is modified to provide sdk volume fakes.
File tests.unit.compute.v2.fakes is modified to provide sdk volume
attachment fakes. For test, setup_sdk_volumes_mock() method is created
so that volumes are created in similar way as servers are created.
Change-Id: I290ba83b6ba27a1377ab73fd0ae06ecced25efd1