lint: fix various linters and a panic with malformed variable bodies

[ryancragun]

This started as a fix for the a nil panic if we run into syntax issues when decoding vars files.

It ended with pleasing new linters that came with the latest version of golangci-lint.

Checklist

• The commit message includes an explanation of the changes
• Manual validation of the changes have been performed (if possible)
• New or modified code has requisite test coverage (if possible)
• I have performed a self-review of the changes
• I have made necessary changes and/or pull requests for documentation
• I have written useful comments in the code