fixes 4725 - fixes deletion of puppet environments with no modules

Without this change, puppet environment would be deleted if for some reason the modules
did not exist on the puppet master in /etc/puppet/environments/

Also new content view versions without puppet modules would not have their environment
changed on the file system to reflect the modules actually in the the repo (none)
Merge pull request #3851 from jlsherrill/env_delete

fixes #4725 - fixes deletion of puppet environments with no modules