Enable clusters to start with the latest version of OCK on libvirt

[zabdulre]

When using the cluster start command, ocne uses the boot.qcow2 on the local file system if it exists. This boot.qcow2 may contain an older version of OCK; a newer version may be available. Pulling and using the latest version of OCK on cluster start should be automatic or at least easy for the user to do. It should not require the user to manually move/delete libvirt volumes.

Things to consider:

• Currently, if a user wants to use the latest version of OCK, they have to start a cluster and update each node to the latest version. Another way a user can use the latest version of OCK is by manually deleting the existing qcow2 and thus force ocne to pull the latest version of OCK. The user is only able to use this method if they do not already have a libvirt cluster running.
• This behavior likely persists even if the user supplies the --boot-volume-container-image flag during cluster start, but this needs to be tested.