[Libguestfs] [PATCH v3] lib: libvirt: Convert all drive socket parameters to an absolute path (RHBZ#1588451).

[Richard W.M. Jones]

https://bugzilla.redhat.com/show_bug.cgi?id=1588451

v2 was here:
https://www.redhat.com/archives/libguestfs/2018-June/msg00067.html

This is a greatly simplified version, which just changes the libvirt
backend to make the path absolute.  None of the tests need to be
adjusted.

Rich.