tests: Fix Python 2.6 compatibility

Recent tests use set comprehension which is available only in Python
2.7, failing builds on EL machines.

Change-Id: Idf684f2dbee3a024d90d7d9fd7378636fad2ea8d
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1132677
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31785
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/32102
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Tested-by: mooli tayer <mtayer@redhat.com>