chore(msk): add ignore-assets pragma to cluster integ test

The MSK module relies on custom resources, which in turn create a Lambda
function with assets. The way the current (lerna/yarn) build works includes
the .ts file (as well as the .d.ts and .js) files in the asset bundle. Using the
new `nozem` build correctly only includes the .d.ts and .js files, leading to a
different asset hash.

Since we don't care about the actual hash anyway, adding the ignore-assets
pragma so this test can pass with either build tool.

packages/@aws-cdk/aws-msk/test/integ.cluster.ts

@@ -1,3 +1,4 @@
+/// !cdk-integ pragma:ignore-assets
 import * as ec2 from '@aws-cdk/aws-ec2';
 import * as cdk from '@aws-cdk/core';
 import * as msk from '../lib';