Fix remote_tmp when become with non admin user (#42396)

* Fix tmpdir on non root become

 - also avoid exception if tmpdir and remote_tmp are None
 - give 'None' on deescalation so tempfile will fallback to it's default behaviour
   and use system dirs
 - fix issue with bad tempdir (not existing/not createable/not writeable)
   i.e nobody and ~/.ansible/tmp
 - added tests for blockfile case

* Revert "Temporarily revert c119d54"

This reverts commit 5c614a59a6.

* changes based on PR feedback and changelog fragment

* changes based on the review

* Fix tmpdir when makedirs failed so we just use the system tmp

* Let missing remote_tmp fail

If remote_tmp is missing then there's something more basic wrong in the
communication from the controller to the module-side.  It's better to
be alerted in this case than to silently ignore it.

jborean and I have independently checked what happens if the user sets
ansible_remote_tmp to empty string and !!null and both cases work fine.
(null is turned into a default value controller-side.  empty string
triggers the warning because it is probably not a directory that the
become user is able to use).

test/units/plugins/action/test_raw.py

@@ -18,11 +18,19 @@
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
+import os
+
 from ansible.errors import AnsibleActionFail
 from ansible.compat.tests import unittest
 from ansible.compat.tests.mock import patch, MagicMock, Mock
 from ansible.plugins.action.raw import ActionModule
 from ansible.playbook.task import Task
+from ansible.plugins.loader import connection_loader
+
+
+play_context = Mock()
+play_context.shell = 'sh'
+connection = connection_loader.get('local', play_context, os.devnull)
 
 
 class TestCopyResultExclude(unittest.TestCase):
@@ -41,10 +49,8 @@ class TestCopyResultExclude(unittest.TestCase):
 
     def test_raw_executable_is_not_empty_string(self):
 
-        play_context = Mock()
         task = MagicMock(Task)
         task.async_val = False
-        connection = Mock()
 
         task.args = {'_raw_params': 'Args1'}
         play_context.check_mode = False
@@ -52,16 +58,15 @@ class TestCopyResultExclude(unittest.TestCase):
         self.mock_am = ActionModule(task, connection, play_context, loader=None, templar=None, shared_loader_obj=None)
         self.mock_am._low_level_execute_command = Mock(return_value={})
         self.mock_am.display = Mock()
+        self.mock_am._admin_users = ['root', 'toor']
 
         self.mock_am.run()
         self.mock_am._low_level_execute_command.assert_called_with('Args1', executable=False)
 
     def test_raw_check_mode_is_True(self):
 
-        play_context = Mock()
         task = MagicMock(Task)
         task.async_val = False
-        connection = Mock()
 
         task.args = {'_raw_params': 'Args1'}
         play_context.check_mode = True
@@ -73,10 +78,8 @@ class TestCopyResultExclude(unittest.TestCase):
 
     def test_raw_test_environment_is_None(self):
 
-        play_context = Mock()
         task = MagicMock(Task)
         task.async_val = False
-        connection = Mock()
 
         task.args = {'_raw_params': 'Args1'}
         task.environment = None
@@ -90,10 +93,8 @@ class TestCopyResultExclude(unittest.TestCase):
 
     def test_raw_task_vars_is_not_None(self):
 
-        play_context = Mock()
         task = MagicMock(Task)
         task.async_val = False
-        connection = Mock()
 
         task.args = {'_raw_params': 'Args1'}
         task.environment = None