feat(ec2): look up VPC from different regions (aws#16728)

- Currently Vpc.fromLookup will default to the Stack's region, when needing to lookup Stack's from other regions (e.g. for VPC peering) this doesn't work and the only other work around is a custom resource
- The lookup provider already supports passing a region and works fine if you pass one that's not the Stack's inferred region, so just propagate that option to the top level
- Fixes aws#10208


----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-ec2/lib/vpc-lookup.ts

@@ -48,4 +48,11 @@ export interface VpcLookupOptions {
    * @default aws-cdk:subnet-name
    */
   readonly subnetGroupNameTag?: string;
+
+  /**
+   * Optional to override inferred region
+   *
+   * @default Current stack's environment region
+   */
+  readonly region?: string;
 }

packages/@aws-cdk/aws-ec2/lib/vpc.ts

@@ -1118,9 +1118,15 @@ export class Vpc extends VpcBase {
       filter.isDefault = options.isDefault ? 'true' : 'false';
     }
 
+    const overrides: {[key: string]: string} = {};
+    if (options.region) {
+      overrides.region = options.region;
+    }
+
     const attributes: cxapi.VpcContextResponse = ContextProvider.getValue(scope, {
       provider: cxschema.ContextProvider.VPC_PROVIDER,
       props: {
+        ...overrides,
         filter,
         returnAsymmetricSubnets: true,
         subnetGroupNameTag: options.subnetGroupNameTag,

packages/@aws-cdk/aws-ec2/test/vpc.from-lookup.test.ts

@@ -250,6 +250,24 @@ describe('vpc from lookup', () => {
       restoreContextProvider(previous);
 
     });
+    test('passes account and region', () => {
+      const previous = mockVpcContextProviderWith({
+        vpcId: 'vpc-1234',
+        subnetGroups: [],
+      }, options => {
+        expect(options.region).toEqual('region-1234');
+      });
+
+      const stack = new Stack();
+      const vpc = Vpc.fromLookup(stack, 'Vpc', {
+        vpcId: 'vpc-1234',
+        region: 'region-1234',
+      });
+
+      expect(vpc.vpcId).toEqual('vpc-1234');
+
+      restoreContextProvider(previous);
+    });
   });
 });