fix(route53): dummy hosted zone has right name

Be sure that the dummy hosted zone props that are returned before
the actual lookup is done have the right domain name already. This is
necessary to make DnsValidateCertificate's validation check succeed.

Fixes #2076.

packages/@aws-cdk/aws-certificatemanager/test/test.dns-validated-certificate.ts

@@ -1,6 +1,6 @@
 import { expect, haveResource } from '@aws-cdk/assert';
-import { PublicHostedZone } from '@aws-cdk/aws-route53';
-import { Stack } from '@aws-cdk/cdk';
+import { HostedZone, PublicHostedZone } from '@aws-cdk/aws-route53';
+import { App, Stack } from '@aws-cdk/cdk';
 import { Test } from 'nodeunit';
 import { DnsValidatedCertificate } from '../lib/dns-validated-certificate';
 
@@ -123,4 +123,35 @@ export = {
       }));
     test.done();
   },
+
+  'works with imported zone'(test: Test) {
+    // GIVEN
+    const app = new App();
+    const stack = new Stack(app, 'Stack', {
+      env: { account: '12345678', region: 'us-blue-5' },
+    });
+    const imported = HostedZone.fromLookup(stack, 'ExampleDotCom', {
+      domainName: 'mydomain.com',
+    });
+
+    // WHEN
+    new DnsValidatedCertificate(stack, 'Cert', {
+      domainName: 'mydomain.com',
+      hostedZone: imported,
+    });
+
+    // THEN
+    expect(stack).to(haveResource('AWS::CloudFormation::CustomResource', {
+        ServiceToken: {
+        'Fn::GetAtt': [
+          'CertCertificateRequestorFunction98FDF273',
+          'Arn'
+          ]
+        },
+        DomainName: 'mydomain.com',
+        HostedZoneId: 'DUMMY'
+      }));
+
+    test.done();
+  },
 };

packages/@aws-cdk/aws-route53/lib/hosted-zone.ts

@@ -75,7 +75,7 @@ export class HostedZone extends Resource implements IHostedZone {
   public static fromLookup(scope: Construct, id: string, query: HostedZoneProviderProps): IHostedZone {
     const DEFAULT_HOSTED_ZONE: HostedZoneContextResponse = {
       Id: '/hostedzone/DUMMY',
-      Name: 'example.com',
+      Name: query.domainName,
     };
 
     interface HostedZoneContextResponse {