Add Linode cloud support.

Ansible support for Linode cloud provider. Rely on linode-python pip library for API calls.

Allows to:
- create server
- delete
- start / stop / restart boxes

Notes and features:
- Can wait for running server
- Idempotence is ensured if linode_id is provided
- default payment term: monthly
- can import public SSH key to root user
- can set root password (need to comply with requirements of Linode API though)
- if no root password provided, it is auto generated
- if no password and no ssh key provided, generated password is returned to the user on creation of a new box
- if no password but ssh key is provided, generated password is NOT returned to the user, the user will have to connect using the SSH key
- plan, datacenter, image, etc. are all using the IDs from the API - no magic here
- default latest kernel is applied to the box, based on the architecture.

Pretty much all the rest is explained in the documentation.

The module can be improved later to support other functions (ex. non Xen kernel, resize box, you name it...)

Cheers!