Implements APIs for VMDK driver

Implements APIs for VMDK driver

- Implemented APIs: create_volume, delete_volume, initialize_connection,
  create_snapthot, delete_snapshot, create_volume_from_snapshot,
  create_cloned_volume
- Modified etc/cinder/cinder.conf.sample adding details for the driver
- Added suds dependency in requirements.txt
- create_volume: does no work. Volume's backing is created lazily
- delete_volume: delete backing if present
- initialize_connection: if backing, not present, create backing, else
  provide backing details to nova to perform attach
  Nova BP/vmware-nova-cinder-support
- create_snapshot: Creates the snapshot of the backing
- delete_snapshot: Deletes the snapshot of the backing
- create_volume_from_snapshot: Creates a full/linked clone from the snapshot
  point in VC. In ESX, copies the VM backing files, registers and reverts to
  the appropriate snapshot point.
- create_cloned_volume: Creates a full/linked clone in VC. In ESX, copies the
  VM backing files and registers as a new backing.
- Written appropriate unit tests
- Work item in BP/vmware-vmdk-cinder-driver

Implements: blueprint vmware-vmdk-cinder-driver
Change-Id: Ib11f2878f8f656209d1ba5e2cbfadae1ac1999b4