Do not prepend default path because it can override modules.

It is common for Puppet to manage itself. If the puppet code you are
deploying pushes files to /etc/puppet/modules/, then prepending this
path can break deployment because it will override the module path if
the deployment code is changing. There is no good reason to include this
path. Puppet has built in defaults for this reason.
Merge pull request #2677 from purpleidea/fix_puppet_apply

provisioner/puppet: do not prepend default path because it can override modules.