fix --volumes[] argument for mussel.sh

mussel arguments which are added by add_args_param() were interpreted to curl command line wrongly.

In functions file, there were some escape missing strings which are supplied to eval.

Example:

```
mussle.sh instance create --volumes[0][size]=10 --volumes[0][type]=shared
```

resulted to:

```
curl -fsSkL --dump-header - -X POST --data-urlencode $\{volumes_args\} --data-urlencode volumes[0][size]=10 http://localhost:9001/api/12.03/instances.yml
```

This is the expected command line comes with this change.

```
curl -fsSkL --dump-header - -X POST --data-urlencode volumes[0][size]=10 http://localhost:9001/api/12.03/instances.yml
```