Add support for vmware_vddk installation

Unless vmware_vddk_url is defined, tasks within 'tasks/vmware_vddk.yml'
will be skipped.  If 'vmware_vddk_url' is defined in groups/all (or via
--extra-vars), the vmware vddk toolkit will be downloaded and installed.
No longer need the install_vddk.sh file
Merge pull request #2 from jlaska/vmware-vddk

Add support for vmware_vddk installation