Making the tests optional

Disabled by default as that's the default behavior we want at the project (run
the tests when you want to run the tests, build the package when you want to
build the package).

Change-Id: I8567b4c93f8b02c448815d4ea853469381a2847f
Signed-off-by: David Caro <dcaroest@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/36122
Reviewed-by: Sandro Bonazzola <sbonazzo@redhat.com>
Reviewed-by: Adam Litke <alitke@redhat.com>