Updates to devstack build profile

- Increase memory of devstack server from 5GB to 7GB
- Update autostack script to reflect upstream changes
  (remove ceilometer hack)
- Disable Neutron, which was preventing VM from provisioning images
- Remove Glance from local.conf; it's already installed by default
- Added instance pre-creation steps to documentation

Change-Id: Ia3259cf440e5f16b194d8339a176f2d919b23bc4