Test a OCI runtime based on a release of runtime-tools

[alban]

So that runtime developers could test their runtime against a specific version of runtime-tools, releases could include the binaries in validation/*.t (and possibly a script to run them).

A release guide should explain how to include the necessary binaries.

[alban]

If that is done, runtimes might want to switch to that at some point in their CI instead of whatever is at git-master:

• Add runtime-tools' validation tests runc#1758
• https://github.com/giuseppe/crun/pull/3

[liangchenye]

It will also be easy to certify a runtime with these scripts.