Allowing to skip checks from command line

We were forcing the value of with_checks in the spec, overriding any value
passed from any external source (rpmmacros, command line, etc.)

Change-Id: Ie7b8ddeb9dec1f54bbed3d9b2945b1e59aeca723
Signed-off-by: David Caro <dcaroest@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35696
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>