Templates: don't quote custom directive values since possible values are constants and would be silently ignored otherwise.

The values to quote should be quoted when defined in sites-cookboks.

Examples:
```
override_attributes(
  'php' =>
    'directives' => {
      'date.timezone' => "'Europe/Paris'",
      'error_reporting' => "E_ALL | E_STRICT",
    }
  }
}
Merge branch 'fix-quoted-values'