openstack_user_config.yml.example mentions that the repo-servers are
optional. This is not the case because we generally rely on it for pip
package installation since liberty. Bypassing it would be a really
specific use case and shouldn't be documented as standard.
Change-Id: I1c78630f1b34adb7dc7be390285123dfd27197bf
Signed-off-by: Jean-Philippe Evrard <jean-philippe.evrard@rackspace.co.uk>