spec: replace requires vdsm-python-cpopen

Due dependency problems and yum bug [1] we are
obsoleting vdsm-python-cpopen with python-cpopen to
avoid installation problem with VDSM.

[1] http://yum.baseurl.org/gitweb?p=yum.git;a=commitdiff;h=1bbf40af8548d2d3fb9deea8844770fccd67a384

Change-Id: Iee2c64d489745db5d0e4a8491d7d8b16dfb1d21b
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/23942
Reviewed-by: Sandro Bonazzola <sbonazzo@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>