VMware: Integrate VMDK driver with oslo.vmware

VMware: Integrate VMDK driver with oslo.vmware

The common code between various VMware drivers was moved to
oslo.vmware library during Icehouse release. The VMDK driver
should be updated to use this library. Changes are mostly
replacing import statements and removing redundant modules
and corresponding test cases.

Summary of changes:
* Replace api with oslo.vmware.api
* Replace vim with oslo.vmware.vim
* Replace pbm with oslo.vmware.pbm
* Replace io_util with oslo.vmware.image_transfer
* Replace vmware_images with oslo.vmware.image_transfer
* Replace read_write_util with oslo.vmware.rw_handles
* Remove error_util and use oslo.vmware.exceptions
* Move VMDK driver specific exceptions to a new module
  'exceptions'
* Replace PBM WSDL files with the corresponding files in
  oslo.vmware
* Replace PBM related methods in volumeops with the
  corresponding ones in oslo.vmware.pbm

Implements: blueprint vmdk-oslo.vmware
Change-Id: Ib484fabffb8ef1a56051d7e1bed5218b633306bb