Use unittest.mock instead of mock

The mock third party library was needed for mock support in py2
runtimes. Since we now only support py36 and later, we can use the
standard lib unittest.mock module instead.

Change-Id: Ib353cf9878334d91e551bf75121413c6fb2222ea

os_collect_config/tests/test_collect.py

@@ -22,7 +22,7 @@ import tempfile
 
 import extras
 import fixtures
-import mock
+from unittest import mock
 from oslo_config import cfg
 import testtools
 from testtools import matchers

os_collect_config/tests/test_config_drive.py

@@ -16,7 +16,7 @@ import os
 import subprocess
 
 import fixtures
-import mock
+from unittest import mock
 import testtools
 
 from os_collect_config import config_drive

os_collect_config/tests/test_ec2.py

@@ -18,7 +18,7 @@ import os
 import uuid
 
 import fixtures
-import mock
+from unittest import mock
 from oslo_config import cfg
 import requests
 import six.moves.urllib.parse as urlparse

os_collect_config/tests/test_zaqar.py

@@ -16,7 +16,7 @@ import json
 
 import fixtures
 from keystoneclient import discover as ks_discover
-import mock
+from unittest import mock
 from oslo_config import cfg
 from oslo_config import fixture as config_fixture
 import testtools

test-requirements.txt

@@ -5,7 +5,6 @@ hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
 fixtures>=3.0.0 # Apache-2.0/BSD
-mock>=2.0.0 # BSD
 python-subunit>=1.0.0 # Apache-2.0/BSD
 sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
 sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4' # BSD