Web publisher for openstack images

This is a basic http publisher for openstack images. After publishing, images
are available in `pulp/openstack/<repo_id>/`.
Remove duplicate 'openstack_image' directory in content dir

Previously, images were saved under
`/some/path/openstack_image/openstack_image/<checksum>/`. This commit removes
the duplicated 'openstack_image' dir.
Merge pull request #6 from beav/webpub

web publisher for images