JCLOUDS-365: ChefSolo should not depend on InstallChefGems

There are two basic ways to install Chef to run Chef Solo: manually installing the Chef gems, or using the Omnibus installer. 

Installing Chef should be a prerequisite for running the ChefSolo statement, and not part/dependency of the statement itself. This will decouple the Solo execution from the way Chef is installed and also allows to customize the installation (for example by configuring a concrete Chef gem version, etc).