Add exoscale provider to libcloud pack

Hi folks, little bit of a dirty hack for Christmas.
This adds the exoscale provider to the libcloud config file.
It modifies the create_vm.py script a bit so we can pass names of image and size
Fixes a typo on the json file for destroy_vm which prevented from destroying vm
Minor readme edit which I made for a test :)

Surely we could create a separate pack for exoscale and cloudstack, but it would also be nice to support everyone through the single libcloud pack.
In this case, we should then at least to something like this:

```python
image['extra'].get('displaytext', image.name)
```

This way we fall-back to image.name if `displaytext` extra attribute is not available.