Fixed RSA key handling of Blueprint Elastic Social GuidCookieHandler

Fixed a bug in the code dealing with the private RSA key for the signed GUID served by com.coremedia.blueprint.elastic.social.cae.guid.GuidCookieHandler that caused OpenJDK newer than 11.0.6 to reject the configured private key if it wasn't created by the CAE itself.

(CMS-17311)