Forward port global environment timeout

Original commit was #a4ec64f by @joshbeard

Docs at https://docs.puppetlabs.com/puppet/latest/reference/environments_configuring.html#environmenttimeout
and testing by Gabe & Gary seem to indicate that we can push the
environment timeout back up to global and omit the `environment.conf`
file.

`modulepath` should also default to `modules:$basemodulepath` per
https://docs.puppetlabs.com/puppet/latest/reference/config_file_environment.html#modulepath

Instructions to undo this commit in case of disaster are being added to
the Troubleshooting Guide.