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).

Discussions with Dave and Jon suggest that we should schedule a sprint item to fix up all our path things and have search paths like you were suggesting. Shall we leave this as it is since it follows the current convention for now and get that work item scheduled.