Use unittest.mock instead of third party mock

Now that we no longer support py27, we can use the standard library
unittest.mock modules instead of the third party mock lib.

Change-Id: I328fd430e61b666147095f860d02a2badcfd3072
Signed-off-by: Sean McGinnis <sean.mcginnis@gmail.com>

openstack_health/tests/test_api.py

@@ -15,11 +15,11 @@
 import datetime
 import json
 import tempfile
+from unittest import mock
 import uuid
 
 from dateutil import parser as date_parser
 import feedparser
-import mock
 import numpy
 from pbr import version
 import six

test-requirements.txt

@@ -6,6 +6,5 @@ hacking<0.11,>=0.10.0
 coverage!=4.4,>=4.0 # Apache-2.0
 docutils>=0.11 # OSI-Approved Open Source, Public Domain
 stestr>=1.0.0 # Apache-2.0
-mock>=2.0 # BSD
 fixtures>=3.0.0 # Apache-2.0/BSD
 feedparser>=5.2.1