[Libcloud-589] ProfitBricks Compute Driver Support

I have completed support for the ProfitBricks compute driver. This adds support for the core compute driver functions against ProfitBricks. The JIRA ticket can be found here:

https://issues.apache.org/jira/browse/LIBCLOUD-589

Let me know if there are any issues or if it can be accepted or not.

Thanks. 
-matt
To make this method more readable and easier to maintain, it would be good to split it into multiple smaller "private" methods.

For example, this part could be split into `def _create_new_datacenter_for_node`, `def _wait_for_datacenter_state(datacenter, state=PROVISIONING_STATE.AVAILABLE)`, etc.