Set KRB5CCNAME so httpd s4u2proxy can with with newer krb5-server
    
    The DIR ccache format is now the default in krb5-server 1.11.2-4
    but /run/user/<uid> isn't created for Apache by anything so it
    has no ccache (and it doesn't have SELinux permissions to write here
    either).
    
    Use KRB5CCNAME to set a file path instead in /etc/sysconfig/httpd.
    
    https://fedorahosted.org/freeipa/ticket/3607