Removed requirement for fedoraUser in auth'ed connections

https://www.pivotaltracker.com/story/show/70306268

Removed the requirement for fedoraUser, but left the hard-coded option there as a fallback configuration.  Now, though, you can configure a Tomcat role in ContainerRolesPrincipalProvider, for instance, and the user with that role doesn't also have to be in the fedoraUser role (or you can have principal configured through an HTTP header from any configured user role, rather than just the fedoraUser one).

You do have to configure the any new role you want to use through BASIC auth in the web.xml file though:

    <auth-constraint>
      <role-name>fedoraUser</role-name>
      <role-name>fedoraAdmin</role-name>
      <role-name>my-new-tomcat-role</role-name>
    </auth-constraint>

I was unable to find a way to make it more dynamic (not require that extra configuration).

If this PR is accepted, a note should be added to https://www.pivotaltracker.com/story/show/70710348, noting this as something else to document.