XenAPI: Inform XAPI who is connecting to it

XenServer supports an 'originator' being passed to the login function
This originator is very useful in identifying how XAPI is being used
and, when there is a problem, which software package issued which
commands

Change-Id: I003979bb3796e870890e220cf4b046e51581a373
Merge "XenAPI: Inform XAPI who is connecting to it"