Add implementation function for getConnectionsOpen()

Author: sharadraju

lib/impl/pool.js

@@ -91,6 +91,15 @@ class PoolImpl {
     errors.throwNotImplemented("getting num connection in use");
   }
 
+  //---------------------------------------------------------------------------
+  // getConnectionsOpen()
+  //
+  // Returns the number of connections opened by the pool.
+  //---------------------------------------------------------------------------
+  getConnectionsOpen() {
+    errors.throwNotImplemented("getting num connection open");
+  }
+
   //---------------------------------------------------------------------------
   // getPoolIncrement()
   //