tests: disable hugepages-pages6 test on ppc architectures

hugepages-pages6 test in qemuxml2argvtest fails on all ppc, ppc64,
and ppc64le with the following error:

libvirt: QEMU Driver error : internal error: hugepage backing not
supported by '/usr/bin/qemu'.

Disable the test by applying this patch for arch in 'ppc ppc64 ppc64le'.

Index: libvirt-1.2.12/tests/qemuxml2argvtest.c
===================================================================
--- libvirt-1.2.12.orig/tests/qemuxml2argvtest.c
+++ libvirt-1.2.12/tests/qemuxml2argvtest.c
@@ -716,7 +716,6 @@ mymain(void)
     DO_TEST_FAILURE("hugepages-pages4", QEMU_CAPS_MEM_PATH,
             QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST("hugepages-pages5", QEMU_CAPS_MEM_PATH);
-    DO_TEST("hugepages-pages6", NONE);
     DO_TEST("nosharepages", QEMU_CAPS_MACHINE_OPT, QEMU_CAPS_MEM_MERGE);
     DO_TEST("disk-cdrom", NONE);
     DO_TEST("disk-cdrom-network-http", QEMU_CAPS_KVM, QEMU_CAPS_DEVICE,