[cgroups2] Do DEBUG container check after creating cgroup for it.

Since we create cgroups for all containers, we will create the DEBUG
container. We expect the DEBUG containers to not have its own resource
contraints, so we will return __prepare early before reaching the
CHECK.

Review: https://reviews.apache.org/r/75172/

src/slave/containerizer/mesos/isolators/cgroups2/cgroups2.cpp

@@ -182,7 +182,6 @@ Future<Option<ContainerLaunchInfo>> Cgroups2IsolatorProcess::prepare(
                    " has already been prepared");
   }
 
-  CHECK(containerConfig.container_class() != ContainerClass::DEBUG);
 
   // Based on MESOS-9305, there seems to be a possibility that the root
   // folder may be deleted underneath us. Since we make use of subtree_control
@@ -232,6 +231,12 @@ Future<Option<ContainerLaunchInfo>> Cgroups2IsolatorProcess::prepare(
   infos[containerId] = Owned<Info>(
       new Info(containerId, nonLeafCgroup, leafCgroup, !shareCgroups));
 
+  if (shareCgroups) {
+    return __prepare(containerId, containerConfig);
+  }
+
+  CHECK(containerConfig.container_class() != ContainerClass::DEBUG);
+
   vector<Future<Nothing>> prepares;
   hashset<string> skip_enable = {"core", "perf_event", "devices"};
   foreachvalue (const Owned<Controller>& controller, controllers) {