[swarm] Draft threaded bridging code

It's not perfect, but it includes some refactoring of the way the
mosquitto broker processes are handled that should be cleaner, so even
though performance and configuration of the threaded version is
terrible, we'll keep this code for now.
[swarm] fab:abort doesn't need a target host

It works perfectly well just killing all the attack processes
[swarm] Support more parameters to beeup for AWS

Make it easier to customize running AWS attack bees from different
zones/AMIs/etc
bridge tls-psk keyfile: Fix off by one in comparison

A 500 entry file is perfectly ok for running 500 clients
[swarm]: AWS: use a default security group that allows ssh

"default" only allows access from other machines in the same group.
[swarm] Properly save region in .malaria

This makes "fab down" work properly
[swarm] Update (still incomplete) swarm docs