Add instructions on bootstrapping puppet-module-data

[jfryman]

After releasing #453, a bug was filed that showed a problem with loading module data. It seems that the new backend does in fact need to be loaded to parse data contained within the module.

Fixes #460

[3flex]

Thanks for clearing this up and sorry for the misleading information - it's weird since I get different results depending on whether I run Puppet directly on command line vs running via Bundler:

Works (loads module_data backend automatically):

bundle exec puppet apply --noop -e 'include nginx'

Doesn't work (doesn't load backend automatically):

puppet apply --noop -e 'include nginx'

As far as I can tell that's the only difference. I tried to do some digging into bundler source and got as far as seeing that it works when I do:

RUBYOPT=-rbundler/setup puppet apply --noop -e 'include nginx'

But my Ruby is basic at best so that's as far as I could get. I'm not sure if there's a bug, and if so, whether it lies with Puppet, Hiera or module_data, but it seems whether it works or not is environment dependent.

One idea floated at http://ttboj.wordpress.com/2014/06/04/hiera-data-in-modules-and-os-independent-puppet/ is a canary - a value set in hiera data which can be tested in the manifest and show an appropriate message if it's not been set and module_data's not working. Just a though, the docs should be OK for now though.

[jfryman]

@3flex no worries! That's interesting to know, and I'll dig into that a bit.

I really like the canary idea. Let's do that. I'll make an issue.