Fix executing CNI addons commands (fixes #594)

[deric]

This PR attempts to fix some changes introduced in #592 and #575.

• Wrap commands in single array
• Don't use double quotes for strings where string interpolation isn't needed
• Avoid unnecessary code duplication

The exec containing command in form

['kubectl', 'get', 'nodes']

will print help message to stdout instead of executing kubectl get nodes.

[puppet-community-rangefinder[bot]]

kubernetes::kube_addons is a class

that may have no external impact to Forge modules.

This module is declared in 0 of 580 indexed public Puppetfiles.

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