knoxsso.redirect.whitelist.regex should not require a port number

The default 'knoxsso.redirect.whitelist.regex' is set to require a port number meaning it won't work for redirects to normal HTTP and HTTPS on :80 and :443:

https://github.com/apache/ambari/blob/trunk/ambari-server/src/main/resources/stacks/HDP/2.5/services/KNOX/configuration/knoxsso-topology.xml#L109-L110

^https?:\/\/(localhost|127\.0\.0\.1|0:0:0:0:0:0:0:1|::1):[0-9].*$

Proposal is to make the port optional and validate that anything after the host or port starts with /.

^https?:\/\/(localhost|127\.0\.0\.1|0:0:0:0:0:0:0:1|::1)(:[0-9]+)?(\/|\/.*)?$

Pull request with the change: https://github.com/apache/ambari/pull/484