Upgrade sensu

DO NOT MERGE

As we dont use something like https://github.com/adrienthebo/r10k, I think the
best way to deploy this will be to deploy from the branch, before merging to 
master

Planned deploy strategy - 

 - Stop sensu on all machines using fabric

 - flush redis

 - deploy sensu to monitoring machine and upgrade it

 - deploy sensu to other machines in environment
I mentioned that in b733e9ca15c2ff44d376baafd676f7b4a3f00867 which referenced sensu/sensu-puppet#184

I dont know enough about rabbit to know what is correct, but without the slash sensu cannot connect to rabbitmq. Helpfully neither rabbit nor sensu are very helpful in their logs as to why this is the case