tools: added cloud.py, which starts an EC2 instance with the Xilinx tools available.

This works towards the goal of CI in EC2.

The script is currently just a shell with placeholders for the parts of the script that actually do the work of building and the like.
At this point, I believe it's starting up. We can check the node's `state` field, which is one of the states defined here: https://libcloud.readthedocs.org/en/latest/compute/api.html#libcloud.compute.types.NodeState.

So far everything has come up in the `PENDING` state, which indicates the instance is starting up.