Use vsphere linked cloning

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #71 from kbarber/vsphere_linked_clone

Use vsphere linked cloning
Release 2.7.0

Signed-off-by: Ken Barber <ken@bob.sh>
Merge branch 'release_270'

* release_270:
  Release 2.7.0