Use unittest.mock instead of third party mock

Now that we don't need to support py27 we can use the standard library
unittest.mock module instead of the third party mock lib.

Change-Id: I1dfdb05ddf78cd8243f31956ccf8173b2059ad33
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

lower-constraints.txt

@@ -17,7 +17,6 @@ keystoneauth1==3.4.0
 linecache2==1.0.0
 MarkupSafe==1.0
 mccabe==0.2.1
-mock==2.0.0
 monotonic==0.6
 mox3==0.20.0
 msgpack-python==0.4.0

pycadf/tests/test_cadf_spec.py

@@ -13,10 +13,9 @@
 # the License.
 
 import time
+from unittest import mock
 import uuid
 
-import mock
-
 from pycadf import attachment
 from pycadf import cadftype
 from pycadf import credential

test-requirements.txt

@@ -8,7 +8,6 @@ flake8-docstrings==0.2.1.post1 # MIT
 coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
 python-subunit>=1.0.0 # Apache-2.0/BSD
-mock>=2.0.0 # BSD
 stestr>=2.0.0 # Apache-2.0
 testtools>=2.2.0 # MIT