host-deploy: getChainFromSSL: acquire chain from session and not negotiation

Although the negotiation seems to be the right place to acquire the
chain, in some cases (such as the one reported in
https://bugzilla.redhat.com/show_bug.cgi?id=1058016 ), it was missing
the root certificate authority, while the chain out of the session is a
complete one.

Change-Id: I397f1341984f78e8fc0a07e9256eeac362b0fcaf
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23773
Reviewed-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>