XENAPI add duration measure to log message

The xenapi snapshot command states when the command completes
but does not put any really useful information in the message itself.
This commit adds the duration the snapshot upload took and
which image was created to the log message.

Change-Id: I684d5152e02f31772ab69e0a8e4931b365a0267c
Merge "XENAPI add duration measure to log message"