Manage config for saving riemann dashboard config to s3.

This is pretty much working, but might need some cleanup to get up to snuff (I'm still relatively new to puppet). One known hole is that the default value for for `use_s3` doesn't work. I don't know how to fix it, but I figure you might (or perhaps my fine fellow udacian, @ods94065, knows how?).

Happy to work out any concerns you have to get this merged, just let me know what needs doing. Would be nice to get #14 in shortly thereafter, too, so we can switch back to using the version from the forge.
It would be best to use `ensure_resource` here rather than explicit packages for fog and ruby-dev.

See the usage here: https://github.com/udacity/garethr-riemann/blob/master/manifests/dash/install.pp#L4

The rationale for using `ensure_resource` is that it won't clash with other modules that might also manage those resources. If you define fog or ruby-dev here it means this module won't work with any other module or manifest that might include those packages.