[COOK-3601] Fixes to get SmartOS working again

https://tickets.opscode.com/browse/COOK-3601

- Updating mnesiadir attribute and copying erlang cookie to /root
so that things work again on SmartOS.
- Reading the erlang cookie file only if it's there
- More tweaks to get user and plugin management working (again) on SmartOS
- Tweaks to clustering setup, plus still fighting with epmd
- Fixing a goof in the rabbitmq.config template
and de-duping definition of the /root/.erlang.cookie template.
- Making some repeated resources unique so that they don't overlap
- Removing a bunch of defaults so that DeepMerge from data bags works as expected
- Making cluster disk node configuration true to its name