Add chaos type: Block all networking

The first new chaos type!  Remove whatever security groups the condemned instance is in, and put it into a new security group which shouldn't allow any traffic.

This means that the instance is still running, but as it isn't accepting network traffic, it is effectively unreachable.  This simulates either a catastrophic network failure or (more likely) some sort of live-crash where the instance is running but the actual service running on that instance has stopped responding.

Either way, good supervising software should detect the "zombie" instance, kill it and replace it.