conpaas-docs: improvements to the installation guide
conpaas-docs: improvements to the installation guide

- Mention Wheezy official ec2 images
- Note that users need to provide a public hostname for the director
- Explain how to add users from the cli
- Update ec2 AMI-IDs


git-svn-id: 3c739b8a310a10be68afd4fdd7f3d450bf1457ba@4908 ef35cc4a-2640-4bbf-98bc-65920db7d8ae

ema/conpaas,ema/conpaas,ema/conpaas,ema/conpaas,ema/conpaas