Add a directory for overcloud heat environments

Add a directory for overcloud heat environments

This patch adds a new directory called environments which contains
custom Heat environment files that can be used to enable custom
overcloud features. As an initial example a puppet-ceph-devel.yaml
environment has been added which can be used to spin up a small Ceph
cluster for dev/testing.

This directory may be useful for collecting other
feature related Heat environment settings in the future as well.
Things like isolated network settings, etc.

Change-Id: Ia6998ae05d2363384d2a616a31d5795c8b2d85d5