Added support for mangle table and fix for chef fail in cases where _chef_lwrp_test chain is left around.

Added support for the mangle table. 

Also have seen a weird bug where certain versions of chef have a known memory leak (http://tickets.opscode.com/browse/CHEF-3432) and leave the _chef_lwrp_test chain behind, meaning the next chef runs fail until it's manually cleaned up. I added the two lines in providers/rule.rb to delete the chain whether it exists or not and ignore the output. Confirmed it works as advertised.