Use node_manager's new purge_behavior parameter

[reidmv]

This allows us to ensure the data we need, but preserve any user data that may have been set, on the node groups we manage.

Depends on puppetlabs/puppetlabs-node_manager#60 being merged and WhatsARanjit-node_manager 0.7.4 being released with an implementation of that feature.

Fixes #130
Closes #133

[puppet-community-rangefinder]

peadm::merge_ng_config_data is a function

that may have no external impact to Forge modules.

peadm::setup::node_manager is a class

that may have no external impact to Forge modules.

This module is declared in 0 of 575 indexed public Puppetfiles.

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