Fix HDFS support for CU5+ BDC instances (#10577)

* Fix HDFS node auth for non-root username

* more changes

extensions/big-data-cluster/src/bdc.d.ts

@@ -0,0 +1,17 @@
+declare module 'bdc' {
+
+	export const enum constants {
+		extensionName = 'Microsoft.big-data-cluster'
+	}
+
+	export interface IExtension {
+		getClusterController(url: string, authType: AuthType, username?: string, password?: string): IClusterController;
+	}
+
+	export type AuthType = 'integrated' | 'basic';
+
+	export interface IClusterController {
+		getClusterConfig(): Promise<any>;
+		getKnoxUsername(clusterUsername: string): Promise<string>;
+	}
+}