Added cloud_properties argument to create_disk

- bumped version to 0.6.0 due to reverse incompatibility
- improved vcloud_cpi_spec error when missing env vars
- added cloud.has_disk? to the unsupported list to make unit tests pass
Merge pull request #6 from karlkfi/master

Added cloud_properties argument to create_disk

- bumped version to 0.6.0 due to reverse incompatibility
- improved vcloud_cpi_spec error when missing env vars
- added cloud.has_disk? to the unsupported list to make unit tests pass