Fix commands for kubectl >= 1.12

The `--username` and `--password` top level options have been removed.

Fortunately we have a backwards compatible way of setting the
credentials via `kubectl config set-credentials <name>`, and using the
`--user <name>` top level option which is available at least in 1.10
(and possibly farther back).

qa/qa/service/kubernetes_cluster.rb

@@ -34,7 +34,14 @@ module QA
         CMD
 
         @api_url = `kubectl config view --minify -o jsonpath='{.clusters[].cluster.server}'`
-        @master_auth = JSON.parse(`gcloud container clusters describe #{cluster_name} --zone #{Runtime::Env.gcloud_zone} --format 'json(masterAuth.username, masterAuth.password)'`)
+
+        @admin_user = "#{cluster_name}-admin"
+        master_auth = JSON.parse(`gcloud container clusters describe #{cluster_name} --zone #{Runtime::Env.gcloud_zone} --format 'json(masterAuth.username, masterAuth.password)'`)
+        shell <<~CMD.tr("\n", ' ')
+          kubectl config set-credentials #{@admin_user}
+          --username #{master_auth['masterAuth']['username']}
+          --password #{master_auth['masterAuth']['password']}
+        CMD
 
         if rbac
           create_service_account
@@ -67,7 +74,7 @@ module QA
 
       def create_service_account
         shell('kubectl create -f -', stdin_data: service_account)
-        shell("kubectl --username #{@master_auth['masterAuth']['username']} --password #{@master_auth['masterAuth']['password']} create -f -", stdin_data: service_account_role_binding)
+        shell("kubectl --user #{@admin_user} create -f -", stdin_data: service_account_role_binding)
       end
 
       def service_account