CA-74544: Associate a username with the sessions xapi passes to SM backends.
CA-74544: Associate a username with the sessions xapi passes to SM backends.

This will appear in the audit log. Formatting is consistent with the
"__dom0__vmpr" username associated with the session passed to the VMPR
plugin.

Signed-off-by: John Else <37b74501daa612e48fea94f9846ed4ddeb6a8f07@citrix.com>

simonjbeaumont/xcp-rrdd,simonjbeaumont/xcp-rrdd,johnelse/xcp-rrdd,djs55/xcp-rrdd,sharady/xcp-networkd,djs55/xcp-networkd,koushikcgit/xcp-networkd,koushikcgit/xcp-rrdd,djs55/xcp-networkd,koushikcgit/xcp-rrdd,johnelse/xcp-rrdd,djs55/xcp-rrdd,koushikcgit/xcp-networkd,sharady/xcp-networkd,koushikcgit/xcp-rrdd