Porting tests to pytest (#33387)

* Porting tests to pytest

* Achievement Get: No longer need mock/generator.py
  * Now done via pytest's parametrization
  * Port safe_eval to pytest
  * Port text tests to pytest
  * Port test_set_mode_if_different to pytest

* Change conftest AnsibleModule fixtures to be more flexible
  * Move the AnsibleModules fixtures to module_utils/conftest.py for sharing
  * Testing the argspec code requires:
    * injecting both the argspec and the arguments.
    * Patching the arguments into sys.stdin at a different level

* More porting to obsolete mock/procenv.py
  * Port run_command to pytest
  * Port known_hosts tests to pytest
  * Port safe_eval to pytest
  * Port test_distribution_version.py to pytest
  * Port test_log to pytest
  * Port test__log_invocation to pytest
  * Remove unneeded import of procenv in test_postgresql

* Port test_pip to pytest style
  * As part of this, create a pytest ansiblemodule fixture in
    modules/conftest.py.  This is slightly different than the
    approach taken in module_utils because here we need to override the
    AnsibleModule that the modules will inherit from instead of one that
    we're instantiating ourselves.

* Fixup usage of parametrization in test_deprecate_warn

* Check that the pip module failed in our test

test/units/module_utils/conftest.py

@@ -0,0 +1,65 @@
+# Copyright (c) 2017 Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+import json
+import sys
+from collections import MutableMapping
+from io import BytesIO
+
+import pytest
+
+import ansible.module_utils.basic
+from ansible.module_utils.six import PY3, string_types
+from ansible.module_utils._text import to_bytes
+
+
+@pytest.fixture
+def stdin(mocker, request):
+    old_args = ansible.module_utils.basic._ANSIBLE_ARGS
+    ansible.module_utils.basic._ANSIBLE_ARGS = None
+    old_argv = sys.argv
+    sys.argv = ['ansible_unittest']
+
+    if isinstance(request.param, string_types):
+        args = request.param
+    elif isinstance(request.param, MutableMapping):
+        if 'ANSIBLE_MODULE_ARGS' not in request.param:
+            request.param = {'ANSIBLE_MODULE_ARGS': request.param}
+        args = json.dumps(request.param)
+    else:
+        raise Exception('Malformed data to the stdin pytest fixture')
+
+    fake_stdin = BytesIO(to_bytes(args, errors='surrogate_or_strict'))
+    if PY3:
+        mocker.patch('ansible.module_utils.basic.sys.stdin', mocker.MagicMock())
+        mocker.patch('ansible.module_utils.basic.sys.stdin.buffer', fake_stdin)
+    else:
+        mocker.patch('ansible.module_utils.basic.sys.stdin', fake_stdin)
+
+    yield fake_stdin
+
+    ansible.module_utils.basic._ANSIBLE_ARGS = old_args
+    sys.argv = old_argv
+
+
+@pytest.fixture
+def am(stdin, request):
+    old_args = ansible.module_utils.basic._ANSIBLE_ARGS
+    ansible.module_utils.basic._ANSIBLE_ARGS = None
+    old_argv = sys.argv
+    sys.argv = ['ansible_unittest']
+
+    argspec = {}
+    if hasattr(request, 'param'):
+        if isinstance(request.param, dict):
+            argspec = request.param
+
+    am = ansible.module_utils.basic.AnsibleModule(
+        argument_spec=argspec,
+    )
+    am._name = 'ansible_unittest'
+
+    yield am
+
+    ansible.module_utils.basic._ANSIBLE_ARGS = old_args
+    sys.argv = old_argv