sbus: Make sbus_new_server() work for non-priveleged processes
    
    I'd like to use this during testing. We should check that the
    socket ownership is the same as the process, rather than limiting
    it to root.
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    (cherry picked from commit e35bff1cf25048a0dcafd6d8fdba60da82e88338)