Add support for VMDK driver

The patch adds support for VMware vmdk cinder driver. It also
supports configuring the driver for multi-backend scenarios.

implements blueprint support-vmdk-driver

(cherry picked from commit 14be6892554ab1c4df6144a0c782bad6b8c9cfec)

Conflicts:
	manifests/volume/vmdk.pp
	spec/classes/cinder_volume_vmdk_spec.rb

Change-Id: Ida0303ac55ab2af5cff9db8fcfcc36d46440c2e2
Merge "Add support for VMDK driver" into stable/havana