history: fixed user usage data collection (#926952)

was collecting the os system user, changed to collect the spice
session user.

Bug-Url: https://bugzilla.redhat.com/926952

Change-Id: I50d4521ef733add0c5439d48c3dbc31bd5ad4e5f
Signed-off-by: Yaniv Dary <ydary@redhat.com>