(MODULES-1096) Fix double quote / single quote issue in params.pp.

To follow style guide advice
(http://docs.puppetlabs.com/guides/style_guide.html#quoting) and make
puppet-lint happy, manifests should only use double quotes with strings that
contain variables.

This commit fixes the lone exception to this rule.
Merge pull request #526 from spil-jaak/bug/master/quote_fixing

(MODULES-1096) Fix double quote / single quote issue in params.pp.