minor fixes to template function
- make sure it calls itself correctly, now passes same params as it recieves
- vars is reserved, changed for templatevars to avoid confustion
- forcing mustaches again since the removal broke 'listification' as per #9622
- fixes incorrectly successful tests using undefined var, now it is defined
- now returns empty list if items is None to avoid errors
fixes issues with listyfing failing too often
Expand playbook_dir in time for loading tasks

Fixes #9618
now only flattened ignores failonundefined cause of it's special need
Merge pull request #9629 from ansible/expand-variables

Expand playbook_dir in time for loading tasks
Update CHANGELOG.md
Merge pull request #9626 from bcoca/minor_template_fixes

fixes to template function
Bumping files for 1.9