e2e: refactor pids isolation tests (#17717)

This PR refactors some old PID isolation tests to make use of the e2e/v3
packages. Should be quite a bit easier to read. Adds 'alloc exec' capability
to the jobs3 package.

e2e/isolation/input/alloc_exec_java.hcl

@@ -0,0 +1,70 @@
+# Copyright (c) HashiCorp, Inc.
+# SPDX-License-Identifier: MPL-2.0
+
+job "java_exec" {
+
+  constraint {
+    attribute = "${attr.kernel.name}"
+    value     = "linux"
+  }
+
+  group "group" {
+
+    update {
+      min_healthy_time = "2s"
+    }
+
+    reschedule {
+      attempts  = 0
+      unlimited = false
+    }
+
+    restart {
+      attempts = 0
+      mode     = "fail"
+    }
+
+    task "build" {
+      lifecycle {
+        hook    = "prestart"
+        sidecar = false
+      }
+
+      driver = "exec"
+      config {
+        command = "javac"
+        args    = ["-d", "${NOMAD_ALLOC_DIR}", "local/Sleep.java"]
+      }
+
+      template {
+        destination = "local/Sleep.java"
+        data        = <<EOH
+public class Sleep {
+    public static void main(String... s) throws Exception {
+        Thread.sleep(999999999);
+    }
+}
+EOH
+      }
+
+      resources {
+        cpu    = 50
+        memory = 64
+      }
+    }
+
+    task "sleep" {
+      driver = "java"
+
+      config {
+        class_path = "${NOMAD_ALLOC_DIR}"
+        class      = "Sleep"
+      }
+
+      resources {
+        cpu    = 50
+        memory = 64
+      }
+    }
+  }
+}