Switch over to mox3

mox3 is the Python 3.x compatible replacement
of mox.

Change-Id: If107d0ebde50d3461505c5f722d53557993f1e7e

heat_cfntools/tests/test_cfn_helper.py

@@ -17,7 +17,7 @@
 import boto.cloudformation as cfn
 import fixtures
 import json
-import mox
+from mox3 import mox
 import os
 import subprocess
 import tempfile

heat_cfntools/tests/test_cfn_hup.py

@@ -14,7 +14,7 @@
 # under the License.
 
 import fixtures
-import mox
+from mox3 import mox
 import tempfile
 import testtools
 

test-requirements.txt

@@ -1,7 +1,7 @@
 # Hacking already pins down pep8, pyflakes and flake8
 hacking>=0.8.0,<0.9
 
-mox>=0.5.3
+mox3>=0.7.0
 discover
 testrepository>=0.0.17
 testtools>=0.9.32