Correct `puppet module list` check in beaker

The final check during the prep stage, where `puppet module list` is
run so that its output can be used for debugging, should run on the
current host in the loop, not the first host in the array. It should
only exit 0.

Change-Id: I5a29908f5c63209dd7416c5e281f60198a4b552c

spec/spec_helper_acceptance.rb

@@ -50,7 +50,7 @@ RSpec.configure do |c|
       on host, "rm -fr #{repo}"
 
       # List modules installed to help with debugging
-      on hosts[0], puppet('module','list'), { :acceptable_exit_codes => [0,1] }
+      on host, puppet('module','list'), { :acceptable_exit_codes => [0] }
     end
   end
 end