Use unittest.mock instead of third party mock

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

Change-Id: I4ef04d18b3a6da5cbf3193330957db7846a7bc8d

test-requirements.txt

@@ -2,7 +2,6 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-mock>=2.0 # BSD
 python-subunit>=0.0.18 # Apache-2.0/BSD
 testtools>=1.4.0 # MIT
 coverage>=3.6 # Apache-2.0

tooz/tests/drivers/test_file.py

@@ -16,9 +16,9 @@
 #    under the License.
 
 import os
+from unittest import mock
 
 import fixtures
-import mock
 from testtools import testcase
 
 import tooz

tooz/tests/test_coordination.py

@@ -16,9 +16,9 @@
 
 import threading
 import time
+from unittest import mock
 
 from concurrent import futures
-import mock
 from six.moves.urllib import parse
 from testtools import matchers
 from testtools import testcase

tooz/tests/test_etcd.py

@@ -14,7 +14,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-import mock
+from unittest import mock
+
 from testtools import testcase
 
 import tooz.coordination

tooz/tests/test_hashring.py

@@ -14,8 +14,8 @@
 #    under the License.
 
 import hashlib
+from unittest import mock
 
-import mock
 from testtools import matchers
 from testtools import testcase
 

tooz/tests/test_memcache.py

@@ -16,11 +16,7 @@
 #    under the License.
 
 import socket
-
-try:
 from unittest import mock
-except ImportError:
-    import mock
 
 from testtools import testcase
 

tooz/tests/test_postgresql.py

@@ -14,11 +14,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-try:
-    # Added in python 3.3+
 from unittest import mock
-except ImportError:
-    import mock
 
 from oslo_utils import encodeutils
 import testtools