[Libguestfs] [PATCH v2] ppc64le: Use -machine cap-htm=off unconditionally

[Richard W.M. Jones]

v1 was here:
https://www.redhat.com/archives/libguestfs/2018-September/thread.html#00000

v2:

 - Make conditional on qemu >= 2.11.2 and libvirt >= 4.6.0.

 - Fix the libvirt XML to match what went upstream.

Still untested.

Rich.