Use beaker-puppet_install_helper to install puppet

When running with BEAKER_provision=no, the following happens:

In Trusty: beaker is running dpkg with '--force' option so even
if Puppet is already installed, the return code will be 0.
In CentOS: beaker is running 'rpm -ivh' the second time and since
the package is already here, the return code will be 1.

Using the new puppet install helper will abort installing puppet
if BEAKER_provision is no, so tests will continue as normal.

Change-Id: I2cb734defce21ed1709e80bd0f0b0d965b772a9d

Gemfile

@@ -18,6 +18,7 @@ group :development, :test do
   gem 'puppet-lint-numericvariable'
 
   gem 'beaker-rspec', :require => false
+  gem 'beaker-puppet_install_helper', :require => false
   gem 'mocha'
   gem 'json'
 end

spec/spec_helper_acceptance.rb

@@ -1,11 +1,7 @@
 require 'beaker-rspec'
+require 'beaker/puppet_install_helper'
 
-hosts.each do |host|
-
-  install_puppet
-
-  on host, "mkdir -p #{host['distmoduledir']}"
-end
+run_puppet_install_helper
 
 RSpec.configure do |c|
   # Project root