enumerate instance in *all* regions (not just us-east-1)

The default boto.ec2 connection is for us-east-1. Enumeration all instances returns only those instances in the region the connection is made to. This version iterates through all the regions available for boto.ec2 connections and then appends their running instances to the same list type returned by the function haproxy_autoscale.get_running_instances(). Confirmed to be backwards compatible, although we might like to mock some tests for future development.