CP-9906: Raise a ref rather than a UUID for VDI_NOT_IN_MAP

The CLI code has the ability to turn the ref into a UUID.

Signed-off-by: John Else <john.else@citrix.com>
CP-9906: Improve SXM failure logging

Log that we don't know to where a VDI should be copied.

Signed-off-by: John Else <john.else@citrix.com>
CP-9906: Improve SXM failure error reporting

Raise a proper Api_error if we've failed to determine the destination to
which a snapshot VDI should be migrated.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1973 from johnelse/sxm-workaround-xs64bit

Improvements to SXM failure logging and error reporting