[Libguestfs] [PATCH nbdkit] v2v: Disable readahead for VMware curl sources too (RHBZ#1848862).

[Richard W.M. Jones]

I'm still testing this fix, so let's hold off the review for the
moment.

Also it may be better to specifically identify problematic servers
rather than disabling this for every curl source.  eg.  I suspect that
the problem is the Java server used by VCenter, so we might think
about only disabling readahead for that single case.

Rich.