Upgrade Tomcat

Previously the Cloud Foundry Java Buildpack used Tomcat 7.0.37 when
hosting web applications.  This version of Tomcat has known
vulnerabilities and therefore needed to be upgraded.  This change
upgrade Tomcat to 7.0.40.

[#49892467]
Merge 49892467-tomcat-upgrade to master

[Completes #49892467]