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

This will need to be pushed as a new gem so that we (Pivotal BOSH team) can complete the create_disk change without breaking vcloud. This change is being made in BOSH to be able to support different kinds of persistent disks in the future, like SSDs (aws) and thin-provisioning (vsphere).

I haven't run the integration or lifecycle tests on the bosh_vcloud_cpi due to not having a vcloud account. 

The BOSH acceptance tests (bats) will need to be run as well, after bumping bosh_vcloud_cpi in the director/micro gemspecs. 

For use with this BOSH branch: 
https://github.com/cloudfoundry/bosh/tree/disk-cloud-properties