test_ipa_subdom_server: Workaround for slow krb5 + SELinux
    
    There is an overhead caused by SELinux after fixing memory leak
    in krb5. https://bugzilla.redhat.com/show_bug.cgi?id=1311287.
    
    The overhead is mainly visible with valgrind and moreover
    it causes failures due to timeouts.
    
    sh$ time libtool --mode=execute ./test_ipa_subdom_server
    
    enabled/permissive SELinux
    real    0m7.976s
    user    0m6.680s
    sys     0m0.189s
    
    disabled SELinux
    real    0m2.111s
    user    0m0.071s
    sys     0m0.043s
    
    valgrind + enabled/permissive SELinux
    real    2m7.310s
    user    2m17.080s
    sys     0m0.786s
    
    valgrind + disabled SELinux
    real    0m5.510s
    user    0m3.396s
    sys     0m0.309s
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    (cherry picked from commit 1510d1264b44c437b8270e0a5a239e8624933c3d)