Add array syntax to Host class for printing puppet config options

Without this, tests either had to guess at the default values (which
can vary across platforms) or run `puppet --configprint`
manually. This code allows test suites to use the nifty
`host.puppet['option']` syntax.
Merge pull request #417 from branan/query_puppet_config_array_syntax

Add array syntax to Host class for printing puppet config options