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.
For common actions, we should use libcloud pack, but if you want more control and access to more provider specific actions, you should use provider specific pack (currently we only have provider specific pack for aws).