test(@angular/cli): cleanup CDK in add material E2E test

Adding material to a project can fail if an incompatible version of the CDK is already present in the project.  This change adjusts the E2E test to include extra package cleanup between test cases.

Author: clydin

tests/legacy-cli/e2e/tests/commands/add/add-material.ts

@@ -1,4 +1,5 @@
 import { expectFileToMatch, rimraf } from '../../../utils/fs';
+import { uninstallPackage } from '../../../utils/packages';
 import { ng } from '../../../utils/process';
 import { isPrereleaseCli } from '../../../utils/project';
 
@@ -25,6 +26,10 @@ export default async function () {
     throw new Error('Installation was not skipped');
   }
 
+  // Clean up existing cdk package
+  // Not doing so can cause adding material to fail if an incompatible cdk is present
+  await uninstallPackage('@angular/cdk');
+
   const output2 = await ng('add', '@angular/material@latest');
   if (output2.stdout.includes('Skipping installation: Package already installed')) {
     throw new Error('Installation should not have been skipped');