Use print_function __future__ import

Rather than continuing to use the old print statement, use the actual
print function introduced in python 2.6. See:

  http://docs.python.org/2/whatsnew/2.6.html#pep-3105-print-as-a-function

Change-Id: I059d982d60e13f13e1caf49509c0fe0b18eda723

tests/unit/test_processutils.py

@@ -15,6 +15,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from __future__ import print_function
+
 from openstack.common import processutils
 from tests import utils