switch to globbed elasticache access to reduce policy size

[mattbucci]

Closes #2 using the solution proposed in mu gitter by @jeffb4

Potential issues were stated as that cfn-nag needed to be more friendly with globs in Feb 2019 on gitter chat

[mneil]

Thanks Matt, yes, cfn nag would error this out if we accepted it without adding in an exception for it to pass. This is a good temporary solution. But long-term I think we need to revisit the size of the yaml files on the mu side to reduce it so that extensions like these are more easily added. I'm not going to merge, but it's good reference if anyone else wants to relax these permissions.