vdsm.spec: Requires python-cpopen >= 1.2.3-4

Previous version of python-cpopen conflicts with vdsm-python-cpopen.
This patch requires a new version of python-cpopen which fix it.

Change-Id: Id0fd3029e02e69797db7194308315d623675bd09
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1020321
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20469
Reviewed-by: Dan Kenigsberg <danken@redhat.com>