Use structured-facts for array values instead of joining them by ,

[coder-hugo]

This PR converts all custom facts that contain array values from string to structured-facts. Btw. this PR will conflict with #118 as both are touching line 31 of lib/facts/gluster.rb. This PR just touches this line as the peer_list fact is already joined within the "calculation" code and not like for the others in the Facter.add section. If #118 will be merged first I'll rebase the PR and fix the merge conflict.