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/module_utils/basic/test_tmpdir.py

@@ -12,7 +12,7 @@ import tempfile
 
 import pytest
 
-from ansible.compat.tests.mock import patch
+from ansible.compat.tests.mock import patch, MagicMock
 
 
 class TestAnsibleModuleTmpDir:
@@ -87,3 +87,25 @@ class TestAnsibleModuleTmpDir:
 
         if not stat_exists:
             assert makedirs['called']
+
+    @pytest.mark.parametrize('stdin', ({"_ansible_tmpdir": None,
+                                        "_ansible_remote_tmp": "$HOME/.test",
+                                        "_ansible_keep_remote_files": True},),
+                             indirect=['stdin'])
+    def test_tmpdir_makedirs_failure(self, am, monkeypatch):
+
+        mock_mkdtemp = MagicMock(return_value="/tmp/path")
+        mock_makedirs = MagicMock(side_effect=OSError("Some OS Error here"))
+
+        monkeypatch.setattr(tempfile, 'mkdtemp', mock_mkdtemp)
+        monkeypatch.setattr(os.path, 'exists', lambda x: False)
+        monkeypatch.setattr(os, 'makedirs', mock_makedirs)
+
+        actual = am.tmpdir
+        assert actual == "/tmp/path"
+        assert mock_makedirs.call_args[0] == (os.path.expanduser(os.path.expandvars("$HOME/.test")),)
+        assert mock_makedirs.call_args[1] == {"mode": 0o700}
+
+        # because makedirs failed the dir should be None so it uses the System tmp
+        assert mock_mkdtemp.call_args[1]['dir'] is None
+        assert mock_mkdtemp.call_args[1]['prefix'].startswith("ansible-moduletmp-")