Allow additional (non-chef) nodes to be specified.

[julianrutten]

The README and commit messages are pretty explanatory, if you have any questions let me know.

[shortdudey123]

FWIW node['munin']['server_list'] already does this

[whatcould]

This is very useful! Would be great to get this in the main fork.

Note that, contrary to the comment above, this does not do the same thing as `node['munin']['server_list'] — that option is for munin-client and specifies what servers are allowed to connect.

This pull request allows you to tell a munin-server to fetch information from other nodes besides those existing in your chef recipe. For example, I have one server I use as a munin server for all my other servers/clusters, rather than setting up a munin server for each separate app; for that server I have to give it a list of nodes.

It's probably clear from the Readme, but here's how nodes are specified:

"nodes": [
      {"fqdn": "myapp-name", "ipaddress": "10.0.0.1"},
      {"fqdn": "anotherapp-name", "ipaddress": "10.0.0.2"},
]