mac address is case sensitive but it's not obvious

This seems to be similar to bug #1353597 but reverse...

When you add a new node using lowercase characters in the mac address it logs an error in /var/log/maas/maas.log

ERROR 2014-08-06 13:25:42,212 maasserver ################################ Exception: {u'mac_addresses': [u'One or more MAC addresses is invalid.']} ################################
ERROR 2014-08-06 13:25:42,212 maasserver Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/django/core/handlers/base.py", line 112, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python2.7/dist-packages/django/views/decorators/vary.py", line 19, in inner_func
    response = func(*args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/piston/resource.py", line 167, in __call__
    result = self.error_handler(e, request, meth, em_format)
  File "/usr/lib/python2.7/dist-packages/piston/resource.py", line 165, in __call__
    result = meth(request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/api_support.py", line 189, in dispatch
    return function(self, request, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/maasserver/api.py", line 576, in new
    return create_node(request)
  File "/usr/lib/python2.7/dist-packages/maasserver/api.py", line 547, in create_node
    raise ValidationError(form.errors)
ValidationError: {u'mac_addresses': [u'One or more MAC addresses is invalid.']}