Java driver supports non-linux targets, so LinuxResources fields isn't
guaranteed to be not-nil.

Task restoring works but dead tasks may be restarted

In tests:
* always cleanup (Kill) the harness
* don't call SetConfig more than once (a race)
* avoid cgroups to allow running without being root

from #4777 comments

Do not register mock_driver on release builds.

client: fingerprint driver plugins

added wrapper struct for plugin.ReattachConfig to better handle serialization