core: Fix log event of proxy host

Adds logging of datacenter or cluster name when one host acts as a proxy
for another one.

Change-Id: Ieb071150cd9da75a8e5025862b650f3eddfaf10a
Bug-Url: https://bugzilla.redhat.com/949469
Signed-off-by: Martin Perina <mperina@redhat.com>