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.
Strangely, we could have the same name but different ids. Exoscale real template names are in display text….this is all a bit hackhish. Don't know if you want to extend this as much as possible for all drivers (ssh keys, userdata, etc…) or create separate packs for each driver.