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.
Can we add something here to wait for some user input or something rather than straight away terminating the machine? Maybe;

```python
finished = ""
while finished != "yes":
   finished = raw_input("Type 'yes' to terminate the instance:").lower()
```