(HC-94) Install hocon gem via puppet

Prior to this commit, the acceptance tests installed the gem via
'gem install'. However 'gem install' is not always available on the
boxes where tests are being run, so install via Puppet instead.

spec/spec_helper_acceptance.rb

@@ -5,11 +5,7 @@
 unless ENV['RS_PROVISION'] == 'no'
   run_puppet_install_helper
   hosts.each do |host|
-    if host[:type] == 'aio'
-      on host, "#{host['privatebindir']}/gem install hocon"
-    else
-      on host, "gem install hocon"
-    end
+    on host, puppet('resource package hocon provider=puppet_gem')
   end
 end