ENH: add 'strict' argument to template module, fail on use of undefined var

I was missing this in recent work, would have saved me some time.

Example play:
```
---
- hosts: local
  connection: local
  gather_facts: no
  tasks:
    -  local_action: template src=template dest=rendered strict=yes
```

template
```
{{ undefined_var }} {{inventory_hostname}}
```

console output with `strict=yes`
```
PLAY [local] ****************************************************************** 

TASK: [template src=t dest=./o strict=yes] ************************************ 
src=template dest=output strict=yes
fatal: [127.0.0.1] => {'msg': "'undefined_var' is undefined", 'failed': True}
fatal: [127.0.0.1] => {'msg': "'undefined_var' is undefined", 'failed': True}
```

Not sure where the double error message is coming from, glad to address
given a pointer.