[V0.4.1 bug fix] Support read K8S config from KUBECONFIG environment variable

docs/KubeflowMode.md

@@ -5,7 +5,7 @@ Now NNI supports running experiment on [Kubeflow](https://github.com/kubeflow/ku
 ## Prerequisite for on-premises Kubernetes Service
 1. A **Kubernetes** cluster using Kubernetes 1.8 or later. Follow this [guideline](https://kubernetes.io/docs/setup/) to set up Kubernetes
 2. Download, set up, and deploy **Kubelow** to your Kubernetes cluster. Follow this [guideline](https://www.kubeflow.org/docs/started/getting-started/) to set up Kubeflow
-3. Prepare a **kubeconfig** file, which will be used by NNI to interact with your kubernetes API server. By default, NNI manager will use $(HOME)/.kube/config as kubeconfig file's path. Refer this [guideline]( https://kubernetes.io/docs/concepts/configuration/organize-cluster-access-kubeconfig) to learn more about kubeconfig. 
+3. Prepare a **kubeconfig** file, which will be used by NNI to interact with your kubernetes API server. By default, NNI manager will use $(HOME)/.kube/config as kubeconfig file's path. You can also specify other kubeconfig files by setting the **KUBECONFIG** environment variable. Refer this [guideline]( https://kubernetes.io/docs/concepts/configuration/organize-cluster-access-kubeconfig) to learn more about kubeconfig. 
 4. If your NNI trial job needs GPU resource, you should follow this [guideline](https://github.com/NVIDIA/k8s-device-plugin) to configure **Nvidia device plugin for Kubernetes**.
 5. Prepare a **NFS server** and export a general purpose mount (we recommend to map your NFS server path in `root_squash option`, otherwise permission issue may raise when nni copy files to NFS. Refer this [page](https://linux.die.net/man/5/exports) to learn what root_squash option is), or **Azure File Storage**. 
 6. Install **NFS client** on the machine where you install NNI and run nnictl to create experiment. Run this command to install NFSv4 client:

src/nni_manager/main.ts

@@ -109,6 +109,7 @@ mkDirP(getLogDir()).then(async () => {
         log.info(`Rest server listening on: ${restServer.endPoint}`);
     } catch (err) {
         log.error(`${err.stack}`);
+        throw err;
     }
 }).catch((err: Error) => {
     console.error(`Failed to create log dir: ${err.stack}`);

src/nni_manager/training_service/kubeflow/kubernetesApiClient.ts

@@ -36,7 +36,7 @@ class GeneralK8sClient {
     protected readonly log: Logger = getLogger();
 
     constructor() {
-        this.client = new K8SClient({ config: K8SConfig.fromKubeconfig(path.join(os.homedir(), '.kube', 'config')), version: '1.9'});
+        this.client = new K8SClient({ config: K8SConfig.fromKubeconfig(), version: '1.9'});
         this.client.loadSpec();
     }
 
@@ -58,7 +58,7 @@ abstract class KubeflowOperatorClient {
     protected crdSchema: any;
 
     constructor() {
-        this.client = new K8SClient({ config: K8SConfig.fromKubeconfig(path.join(os.homedir(), '.kube', 'config'))});
+        this.client = new K8SClient({ config: K8SConfig.fromKubeconfig() });
         this.client.loadSpec();
     }