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: I14b6d65b5a6560456b9110de667f94f5d6c9bd20

lower-constraints.txt

@@ -29,7 +29,6 @@ keystoneauth1==3.4.0
 linecache2==1.0.0
 MarkupSafe==1.0
 mccabe==0.2.1
-mock==2.0.0
 monotonic==0.6
 msgpack-python==0.4.0
 munch==2.1.0

searchlightclient/tests/unit/osc/v1/fakes.py

@@ -13,7 +13,7 @@
 #   under the License.
 #
 
-import mock
+from unittest import mock
 
 from searchlightclient.tests.unit.osc import fakes
 from searchlightclient.tests.unit.osc import utils

searchlightclient/tests/unit/v1/test_facets.py

@@ -12,8 +12,8 @@
 
 from searchlightclient.v1 import facets
 
-import mock
 import testtools
+from unittest import mock
 
 
 class FacetsManagerTest(testtools.TestCase):

searchlightclient/tests/unit/v1/test_resource_types.py

@@ -12,8 +12,8 @@
 
 from searchlightclient.v1 import resource_types
 
-import mock
 import testtools
+from unittest import mock
 
 
 class ResourceTypeManagerTest(testtools.TestCase):

searchlightclient/tests/unit/v1/test_search.py

@@ -12,8 +12,8 @@
 
 from searchlightclient.v1 import search
 
-import mock
 import testtools
+from unittest import mock
 
 
 class SearchManagerTest(testtools.TestCase):

test-requirements.txt

@@ -6,6 +6,5 @@
 hacking>=3.0,<3.1.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
-mock>=2.0.0 # BSD
 stestr>=2.0.0 # Apache-2.0
 testtools>=2.2.0 # MIT