python: Fix print function compatibility.

The print statement from Python 2 is a function in Python 3.  Enable
print function support for Python 2 and convert print statements to
function calls.

Enable the H233 flake8 warning.  If the hacking plugin is installed,
this will generate warnings for print statement usage not compatible
with Python 3.

  H233 Python 3.x incompatible use of print operator

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>

tests/test-json.py

@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import print_function
+
 import codecs
 import getopt
 import sys
@@ -21,7 +23,7 @@ import ovs.json
 
 def print_json(json):
     if type(json) in [str, unicode]:
-        print "error: %s" % json
+        print("error: %s" % json)
         return False
     else:
         ovs.json.to_stream(json, sys.stdout)