tests: Avoid printing objects that reference None

One of the current ioprocess tests checks who holds reference to the
ioprocess object, but since only a weak reference is stored, if the
object is freed, we check who holds reference to None, and apparently
quite a lot things do.

Change-Id: I9770873d70ec962837574fe32e8b4cb613e7c696
Signed-off-by: Dima Kuznetsov <dkuznets@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34978
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Yeela Kaplan <ykaplan@redhat.com>
Tested-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>