Add DNS records for bootstrapped EC2 instances. This should remove the need
to keep dev environments in sync by modifying hosts files, and puts us
on the path to making the rest of the config management less brittle, too.

the new 'ec2_hosts' directory is an example of using a dir to hold
multiple inventories in ansible. Needed to do this in order to make
both ec2 instances and localhost available as hosts in the bootstrap
playbook, and to put the virtualenv python path in.