chore(aws-ec2): fix broken integration tests (#19690)

Couple of fixes:

- `integ.instance-init`: Create a new VPC instead of performing a lookup
  in order to make the stack env agnostic
- `integ.vpc-endpoint-service`: Moved this test to the
  elasticloadbalancingv2 package since for the test to actually do
  anything it needs to create NLBs.
- `integ.vpc-endpoint-service-cn`: Removed this test since it is the
  same as the above test except for creating it in china
- `integ.vpc-flow-logs`: Added `autoDeleteObjects` so that the stack can
  be deleted. Also added the bucket policy to the bucket to avoid some
  race conditions when the stack tries to delete the bucket while AWS is
  attempting to add this policy to the bucket.
- `integ.vpn-pre-shared-key-token`: The purpose of this test seemed to
  be validating that a token can be used so I changed this to just use
  `Lazy`. Also, that property does not support SSM Secure references.


----

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### New Features

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packages/@aws-cdk/aws-ec2/test/integ.instance-init.ts

@@ -5,14 +5,9 @@ import * as cdk from '@aws-cdk/core';
 import * as ec2 from '../lib';
 
 const app = new cdk.App();
-const stack = new cdk.Stack(app, 'integ-init', {
-  env: {
-    account: process.env.CDK_INTEG_ACCOUNT || process.env.CDK_DEFAULT_ACCOUNT,
-    region: process.env.CDK_INTEG_REGION || process.env.CDK_DEFAULT_REGION,
-  },
-});
+const stack = new cdk.Stack(app, 'integ-init');
 
-const vpc = ec2.Vpc.fromLookup(stack, 'VPC', { isDefault: true });
+const vpc = new ec2.Vpc(stack, 'IntegInitVpc');
 
 const tmpDir = fs.mkdtempSync('/tmp/cfn-init-test');
 fs.writeFileSync(path.resolve(tmpDir, 'testFile'), 'Hello World!\n');