attribute export_locations is a string

[frank]

The attribute `export_locations` of a `OS::Manila::Share` is a string

Expected: `export_locations` is a list

Example to reproduce:

```yaml
heat_template_version: wallaby

resources:
  share:
    type: OS::Manila::Share
    properties:
      share_protocol: NFS
      share_type: CephNFS
      size: 1

outputs:
  export_locations:
    value: {get_attr: [share, export_locations]}
  first_element:
    value: {get_attr: [share, export_locations, 0]}
```

Output:

```
+------------------+------------------------------------------+
| Field | Value |
+-------------------------------------------------------------+
| export_locations | { |
| | "output_key": "export_locations", |
| | "description": "No description given", |
| | "output_value": "['IP:path']" |
| | } |
| first_element | { |
| | "output_key": "first_element", |
| | "description": "No description given", |
| | "output_value": "[" |
| | } |
+-------------------------------------------------------------+
```

[frank (frank-berghaus)]

Posted this on: https://storyboard.openstack.org/#!/story/2011146