Crash on custom kernel debugger

[mgrabovsky]

When retracing vmcores using the Podman backend, Retrace Server doesn't support custom kernel debuggers correctly. Given a custom KernelDebuggerPath:

$ grep gitlab-runner /etc/retrace-server/retrace-server.conf
KernelDebuggerPath = /cores/crashext/gitlab-runner/bin/crash

a vmcore task fails with

Error: exec failed: container_linux.go:370: starting container process caused: exec: "/cores/crashext/gitlab-runner/bin/crash": stat /cores/crashext/gitlab-runner/bin/crash: no such file or directory: OCI not found

Reported by @DaveWysochanskiRH.