Fix installutils.get_password without a TTY
    
    If stdin is a TTY, ipaserver.install.installutils uses getpass and all
    is well. Without a TTY, though, there were two problems:
    
    * The prompt was not printed
    * On end of file, an empty string was returned, which caused read_password
      to enter an infinite loop.
    
    Fix both problems.
    
    https://fedorahosted.org/freeipa/ticket/3824