CA-177418: Create VDIs with uuids provided by the vdi_info
CA-177418: Create VDIs with uuids provided by the vdi_info

If the storage backend provides a vdi_info.uuid, use this to generate
the uuid, otherwise generate a fresh uuid. In no circumstances do we
treat the key (which could be anything, like a filename) as a uuid.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

jjd27/xen-api,euanh/xen-api,simonjbeaumont/xen-api,simonjbeaumont/xen-api,jjd27/xen-api,salvocambria/xen-api,anoobs/xen-api,salvocambria/xen-api,thomassa/xen-api,guard163/xen-api,robertbreker/xen-api,jjd27/xen-api,simonjbeaumont/xen-api,anoobs/xen-api,robertbreker/xen-api,jjd27/xen-api,euanh/xen-api,agimofcarmen/xen-api,Frezzle/xen-api,djs55/xen-api,salvocambria/xen-api,agimofcarmen/xen-api,srowe/xen-api,srowe/xen-api,djs55/xen-api,robertbreker/xen-api,rafalmiel/xen-api,jjd27/xen-api,djs55/xen-api,anoobs/xen-api,djs55/xen-api,robertbreker/xen-api,guard163/xen-api,agimofcarmen/xen-api,srowe/xen-api,euanh/xen-api,Frezzle/xen-api,robertbreker/xen-api,thomassa/xen-api,djs55/xen-api,guard163/xen-api,jjd27/xen-api,Frezzle/xen-api,rafalmiel/xen-api,thomassa/xen-api,rafalmiel/xen-api,euanh/xen-api,euanh/xen-api,Frezzle/xen-api,simonjbeaumont/xen-api,thomassa/xen-api,euanh/xen-api,anoobs/xen-api,rafalmiel/xen-api,salvocambria/xen-api,guard163/xen-api,rafalmiel/xen-api,robertbreker/xen-api,salvocambria/xen-api,thomassa/xen-api,vasilenkomike/xen-api,salvocambria/xen-api,srowe/xen-api,guard163/xen-api,simonjbeaumont/xen-api,djs55/xen-api,simonjbeaumont/xen-api,anoobs/xen-api,agimofcarmen/xen-api,anoobs/xen-api,vasilenkomike/xen-api,agimofcarmen/xen-api,Frezzle/xen-api,rafalmiel/xen-api,vasilenkomike/xen-api,vasilenkomike/xen-api,srowe/xen-api,vasilenkomike/xen-api,vasilenkomike/xen-api,guard163/xen-api,thomassa/xen-api,agimofcarmen/xen-api