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).

lib/ansible/modules/files/assemble.py

@@ -107,9 +107,9 @@ from ansible.module_utils.six import b
 from ansible.module_utils._text import to_native
 
 
-def assemble_from_fragments(src_path, delimiter=None, compiled_regexp=None, ignore_hidden=False):
+def assemble_from_fragments(src_path, delimiter=None, compiled_regexp=None, ignore_hidden=False, tmpdir=None):
     ''' assemble a file from a directory of fragments '''
-    tmpfd, temp_path = tempfile.mkstemp()
+    tmpfd, temp_path = tempfile.mkstemp(dir=tmpdir)
     tmp = os.fdopen(tmpfd, 'wb')
     delimit_me = False
     add_newline = False
@@ -204,7 +204,7 @@ def main():
     if validate and "%s" not in validate:
         module.fail_json(msg="validate must contain %%s: %s" % validate)
 
-    path = assemble_from_fragments(src, delimiter, compiled_regexp, ignore_hidden)
+    path = assemble_from_fragments(src, delimiter, compiled_regexp, ignore_hidden, module.tmpdir)
     path_hash = module.sha1(path)
     result['checksum'] = path_hash
 

lib/ansible/modules/files/blockinfile.py

@@ -160,7 +160,7 @@ from ansible.module_utils._text import to_bytes
 
 def write_changes(module, contents, path):
 
-    tmpfd, tmpfile = tempfile.mkstemp()
+    tmpfd, tmpfile = tempfile.mkstemp(dir=module.tmpdir)
     f = os.fdopen(tmpfd, 'wb')
     f.write(contents)
     f.close()

lib/ansible/modules/files/replace.py

@@ -154,7 +154,7 @@ from ansible.module_utils.basic import AnsibleModule
 
 def write_changes(module, contents, path):
 
-    tmpfd, tmpfile = tempfile.mkstemp()
+    tmpfd, tmpfile = tempfile.mkstemp(dir=module.tmpdir)
     f = os.fdopen(tmpfd, 'wb')
     f.write(contents)
     f.close()