Comment 2 for bug 1419043

Looking at the code in:

http://git.openstack.org/cgit/openstack/keystone/tree/keystone/assignment/core.py#n236

It looks to me like if there are 2 incoming requests for a new user requests at roughly the same time and the role hasn't been created yet the 2 requests will race to create the role. I'll push out a fix soon that'll just add a lock to make sure this doesn't happen and only one can create the role.