Make the verifyDnsConfig() api return the valid credentials

src/dns/digitalocean.js

@@ -179,16 +179,21 @@ function verifyDnsConfig(dnsConfig, domain, ip, callback) {
     assert.strictEqual(typeof ip, 'string');
     assert.strictEqual(typeof callback, 'function');
 
+    var credentials = {
+        provider: dnsConfig.provider,
+        token: dnsConfig.token
+    };
+
     dns.resolveNs(domain, function (error, nameservers) {
         if (error && error.code === 'ENOTFOUND') return callback(new SubdomainError(SubdomainError.BAD_FIELD, 'Unable to resolve nameservers for this domain'));
         if (error || !nameservers) return callback(error || new Error('Unable to get nameservers'));
 
-        upsert(dnsConfig, domain, 'my', 'A', [ ip ], function (error, changeId) {
+        upsert(credentials, domain, 'my', 'A', [ ip ], function (error, changeId) {
             if (error) return callback(new SubdomainError(SubdomainError.INTERNAL_ERROR, error));
 
             debug('verifyDnsConfig: A record added with change id %s', changeId);
 
-            callback();
+            callback(null, credentials);
         });
     });
 }