(QENG-1186) Fix Beaker::DSL:Helpers.puppet_{user,group}

Looks like the contents of these methods were mixed upwhen originally written.
Luckily the puppet user is usually the same as the puppet group.

Signed-off-by: Wayne <wayne@puppetlabs.com>
Merge pull request #445 from waynr/fix/qeng-1186-beaker-dsl-helpers-puppet-mixup

(QENG-1186) Fix Beaker::DSL:Helpers.puppet_{user,group}