Rename update_snapshot_info -> update_snapshot_info_src

Signed-off-by: John Else <john.else@citrix.com>
Fix partial application

Signed-off-by: John Else <john.else@citrix.com>
Better logging for update_snapshot_info_src

Signed-off-by: John Else <john.else@citrix.com>
Add SMAPI call update_snapshot_info_dest

Signed-off-by: John Else <john.else@citrix.com>
Rearrange snapshot updating SMAPI code

- Implement SR.update_snapshot_info_dest
- Call the above from SR.update_snapshot_info_src
- Remove VDI.set_snapshot_of, VDI.set_snapshot_time,
  VDI.set_is_a_snapshot from SMAPI

Signed-off-by: John Else <john.else@citrix.com>