Move unit test compat code out of lib/ansible/. (#46996)

* Move ansible.compat.tests to test/units/compat/.
* Fix unit test references to ansible.compat.tests.
* Move builtins compat to separate file.
* Fix classification of test/units/compat/ dir.

test/units/modules/system/interfaces_file/test_interfaces_file.py

@@ -15,7 +15,7 @@
 # You should have received a copy of the GNU General Public License
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
-from ansible.compat.tests import unittest
+from units.compat import unittest
 from ansible.modules.system import interfaces_file
 import os
 import json

test/units/modules/system/test_iptables.py

@@ -1,4 +1,4 @@
-from ansible.compat.tests.mock import patch
+from units.compat.mock import patch
 from ansible.module_utils import basic
 from ansible.modules.system import iptables
 from units.modules.utils import AnsibleExitJson, AnsibleFailJson, ModuleTestCase, set_module_args

test/units/modules/system/test_java_keystore.py

@@ -8,8 +8,8 @@
 import os
 
 from units.modules.utils import ModuleTestCase, set_module_args
-from ansible.compat.tests.mock import patch
-from ansible.compat.tests.mock import Mock
+from units.compat.mock import patch
+from units.compat.mock import Mock
 from ansible.module_utils.basic import AnsibleModule
 from ansible.modules.system.java_keystore import create_jks, cert_changed, ArgumentSpec
 

test/units/modules/system/test_known_hosts.py

@@ -2,7 +2,7 @@ import os
 import tempfile
 import ansible.module_utils.basic as basic
 
-from ansible.compat.tests import unittest
+from units.compat import unittest
 from ansible.module_utils._text import to_bytes
 from ansible.module_utils.basic import AnsibleModule
 

test/units/modules/system/test_linux_mountinfo.py

@@ -1,7 +1,7 @@
 import os
 import tempfile
 
-from ansible.compat.tests import unittest
+from units.compat import unittest
 from ansible.module_utils._text import to_bytes
 
 from ansible.modules.system.mount import get_linux_mounts

test/units/modules/system/test_pamd.py

@@ -1,5 +1,5 @@
 from __future__ import (absolute_import, division, print_function)
-from ansible.compat.tests import unittest
+from units.compat import unittest
 
 from ansible.modules.system.pamd import PamdRule
 from ansible.modules.system.pamd import PamdLine

test/units/modules/system/test_parted.py

@@ -16,7 +16,7 @@
 # along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
 
 __metaclass__ = type
-from ansible.compat.tests.mock import patch, call
+from units.compat.mock import patch, call
 from ansible.modules.system import parted as parted_module
 from ansible.modules.system.parted import parse_partition_info
 from units.modules.utils import AnsibleExitJson, AnsibleFailJson, ModuleTestCase, set_module_args

test/units/modules/system/test_systemd.py

@@ -1,7 +1,7 @@
 import os
 import tempfile
 
-from ansible.compat.tests import unittest
+from units.compat import unittest
 from ansible.modules.system.systemd import parse_systemctl_show