Use modulepath for Puppet

Use modulepath for Puppet

We only create the /etc/puppet/modules symlinks during image building,
so as we update the openstack-puppet-modules RPM during the lifecycle
of a deployment, the symlinks can get out of date and some modules
aren't find.

This patch adds modulepath for puppet deployments, getting rid of the
need for our Puppet modules to be symlinked from /etc/puppet/modules. If
there are some already symlinked, they will take precedence. Also
modules installed from source to /opt/stack/puppet-modules will take
precedence over packaged modules in /usr/share/openstack-puppet/modules.

Change-Id: I626a596478be7c55500f9e3c7118ef64ff28aaae
Closes-Bug: #1613211