Fix cookie processing for RDAP URL update (#630)

* Fix cookie processing for RDAP URL update

The existing code only does cookie processing on the _first_ Set-Cookie
header.  Therefore, if the "id" cookie used for authentication is defined in
anything other than the first Set-Cookie header (as it now is), we don't find
it.

Replace the cookie processing stanza with a line that processes all cookies in
all Set-Cookie headers.

core/src/test/java/google/registry/rdap/UpdateRegistrarRdapBaseUrlsActionTest.java

@@ -319,6 +319,10 @@ public final class UpdateRegistrarRdapBaseUrlsActionTest extends ShardableTestCa
 
   private static void addValidResponses(TestHttpTransport httpTransport) {
     MockLowLevelHttpResponse loginResponse = new MockLowLevelHttpResponse();
+    loginResponse.addHeader(
+        "Set-Cookie",
+        "JSESSIONID=bogusid; "
+            + "Expires=Tue, 11-Jun-2019 16:34:21 GMT; Path=/; Secure; HttpOnly");
     loginResponse.addHeader(
         "Set-Cookie",
         "id=myAuthenticationId; "