fix variable access by 'variable_name' is deprecated .

Access to variables in templates using only variable_name is
deprecated, we should use @variable_name instead.

This commit fix this issue in nrpe puppet module.
- Changed CentOS box' URL in Vagrantfile because the original box provided by Dropbox is no longer accessiable. Dropbox responds with a 509.
- Updated Vagrantfile to Vagrant's config version 2. Reason: The current Vagrant release 1.3.5 printed a lot of warnings while operating upon a version 1 config.
Merge pull request #9 from ogm256/master

- Changed CentOS box' URL in Vagrantfile because the original box provid...
Fix Package[nrpe_packages]: Name must be a String not Array
Make subnet configurable

Taken from PR2 by @s0enke, rebased with small mods.
Merge pull request #8 from lmello/fix_deprecated_variable_warning

fix variable access by 'variable_name' is deprecated .
Merge pull request #11 from croomes/fix_redis_host

Make subnet configurable
Merge pull request #10 from croomes/fix_string_not_array

Fix Package[nrpe_packages]: Name must be a String not Array