Change behaviour to align with vanilla Keystone

The current code enforces that the tenant name is the same as the VO
name. This code removes this constrain, so that the user should use the
tenant discovery to get his tenant in advance.
Move code to keystone_voms.core and update docs

The code has been moved to keystone_voms/core.py so that it is not
anymore in __init__.py

The documentation has been updated to reflect the latest changes.
Update tests to work with Grizzly.

The unittests can now be executed against a Grizzly environment. Added
instructions to run them.
Merge pull request #4 from alvarolopez/remove_tenant_constraints

Remove tenant constraints
Added help to options and fixed sample configuration
Bump version to 2013.1-1 and added download_url
Check for user membership in mapped tenant

If the autocreate users option is set we sould add the user in each of
the tenats that he is able to access.

Fixes bug 1
Add unittest for bug/1
Merge pull request #1 from alvarolopez/bug/1

Membership in various tenants/VOs is not handled correctly