update tomcat's defaults to trust 172.16/12 networks as internal proxies

Fairly common use case is to deploy CF in a 172.16/12 network. Tomcat (used by identity) does not recognize this subnet by default, but it can be configured. The following commit, simply adds 172.16/12 to tomcat's default.

Tomcat by default supports, 10/8, 192.168/16, 169.254/16 and 127/8. We've added the regex 172.1[6-9]{1}.\d{1,3}.\d{1,3}|172.2[0-9]{1}.\d{1,3}.\d{1,3}|172.3[0-1]{1}.\d{1,3}.\d{1,3} to support the 172.16/12 range see - http://tomcat.apache.org/tomcat-7.0-doc/api/org/apache/catalina/valves/RemoteIpValve.html