CP-8988: Support environments without suspend image conversion tools

This has been tested on a https://github.com/xenserver/buildroot environment running with a version of xenguest supporting the `-supports` option (https://github.com/xapi-project/ocaml-xen-lowlevel-libs/commit/6495760c0a711e10fe8428d3a9057999910ae057).

Well, it will only ever exist on a 64-bit system AFAIK. I think all these paths are override-able(?) in xenopsd.conf and these refs should be set to where they should 'normally' be. But it raises the point that I should probably stick it in the config as well.