Add VDI.set_content_id

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Add VDI.{add_to,remove_from}_sm_config

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #19 from djs55/set-content-id

Implement more storage motion stuff
Release 0.9.20

Signed-off-by: David Scott <dave.scott@eu.citrix.com>