use ensure_packages

[globin]

The module should use puppetlabs-stdlib's ensure_packages to avoid packages being declared multiple times.

(https://github.com/puppetlabs/puppetlabs-stdlib#ensure_packages)

[shivapoudel]

patches welcome!

[rcmachado]

Just in case, some criticisms about ensure_packages: https://groups.google.com/forum/#!topic/puppet-users/OF_WYN41dMI