raw_exec leaks child process if executor fails (Linux)

[tgross]

While debugging #23668 for Windows, I wanted to see how similar behavior works for Linux. Unfortunately if the executor is killed on Linux we get similar but not identical results. In that case the child process is leaked but when the allocation is marked failed we end up cleaning it up. That cleanup itself seems a little dubious.

Simple reproduction is to run something simple like:

job "example" {

  group "web" {

    task "http" {

      driver = "raw_exec"

      config {
        command = "/usr/bin/busybox"
        args    = ["httpd", "-v", "-f", "-p", "8001", "-h", "/tmp"]
      }

      resources {
        cpu    = 100
        memory = 100
      }

    }
  }
}

Use ps to find the executor process and kill -9 it.