add multicast support. fix various brokenness

This patch adds multicast-based clustering/session replication support. It also fixes some issues I found in testing tomcat6 and tomcat7 (from http://ftp.pbone.net/mirror/www.jpackage.org/jpackage/6.0/generic/free/ on CentOS6) on CentOS6 and Ubuntu14.04.

I've signed the CLA as 'elijahbuck', but I don't know where you are on the transition to a pure-GitHub process. Do I need to create a ticket in JIRA?

Changes are:

* Adds four attributes, cluster_multicast_*
* Ubuntu 14.04 tomcat 6 doesn't have catlina.policy, it has policy.d
* 'bin/' and 'lib/' are under #{node['tomcat']['home']} in ubuntu and redhat. They are not under "#{node['tomcat']['base]} on ubuntu.
* webapp_dir is already at "#{new_resource.base}/#{name}" on ubuntu 14.04, so we can't create a symlink to it.
* The tomcat init scripts on CentOS expect /usr/sbin/tomcat6 or /usr/sbin/dtomcat7, and the init script copy blindly replaces 'tomcat<version>' with 'tomcat<version>-<instance>', which breaks the init script. So, we create a link to the init script with the 'mangled' name.
* The xml elements in server.xml should be terminated with '/>' even if redirectPort isn't defined.