Version-Release number of selected component (if applicable):
0.9.2

Steps to Reproduce:
1. Add a distro tree URL whose scheme is not nfs:// http:// or ftp:// (for example, nfs+iso://)
2. Provision the distro tree without specifying method in ksmeta
  
Actual results:
2012-08-13 16:41:45,875 beakerd ERROR Failed to provision recipeid 80
Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/bkr/server/tools/beakerd.py", line 454, in scheduled_recipes
    recipe.provision()
  File "/usr/lib/python2.6/site-packages/bkr/server/model.py", line 4971, in provision
    recipe=self, ks_appends=ks_appends)
  File "/usr/lib/python2.6/site-packages/bkr/server/kickstart.py", line 158, in generate_kickstart
    result = template.render(context)
  File "/usr/lib64/python2.6/site-packages/jinja2/environment.py", line 669, in render
    return self.environment.handle_exception(exc_info, True)
  File "/usr/lib/python2.6/site-packages/bkr/server/kickstarts/Fedora", line 7, in top-level template code
    {{ snippet('install_method') }}
  File "/usr/lib64/python2.6/site-packages/jinja2/sandbox.py", line 251, in call
    return __context.call(__obj, *args, **kwargs)
  File "/usr/lib/python2.6/site-packages/bkr/server/kickstart.py", line 145, in snippet
    return template.render(context)
  File "/usr/lib64/python2.6/site-packages/jinja2/environment.py", line 669, in render
    return self.environment.handle_exception(exc_info, True)
  File "/usr/lib/python2.6/site-packages/bkr/server/snippets/install_method", line 1, in top-level template code
    {% set url = distro_tree.url_in_lab(system.lab_controller, scheme=method|default(None), required=True) %}
  File "/usr/lib64/python2.6/site-packages/jinja2/sandbox.py", line 251, in call
    return __context.call(__obj, *args, **kwargs)
  File "/usr/lib/python2.6/site-packages/bkr/server/model.py", line 3012, in url_in_lab
    return sorted(urls, key=lambda url: scheme_order.index(urlparse.urlparse(url).scheme))[0]
  File "/usr/lib/python2.6/site-packages/bkr/server/model.py", line 3012, in <lambda>
    return sorted(urls, key=lambda url: scheme_order.index(urlparse.urlparse(url).scheme))[0]
ValueError: list.index(x): x not in list

Expected results:
No breakage