This adds the ability to update the headers in a VHDX image, including
generating a new MS-compatible GUID.
As VHDX depends on uuid.h, VHDX is now a configurable build option. If
VHDX support is enabled, that will also enable uuid as well. The
default is to have VHDX enabled.
To enable/disable VHDX: --enable-vhdx, --disable-vhdx
Signed-off-by: Jeff Cody <jcody@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>