Make init_style can be disabled

In case install consul from package, the start up script will be
included in the packaging system. Give an option to disable the
init_style so that user can leverage the start script from package.
Require Bundler.setup to make rspec work

To load rspec-puppet which is downdoaded from github for testing, it
needs require 'bundler/setup' in order to load the bundler path.