Enable new go linters and fix the existing issues

[khos2ow]

Prerequisites

Put an x into the box(es) that apply:

• This pull request fixes a bug.
• This pull request adds a feature.
• This pull request enhances existing functionality.
• This pull request introduces breaking change.

For more information, see the Contributing Guide.

Description

This PR enables new go linters and fixes the existing issues for some of them. The list of enabled linters are:

• govet
• golint
• misspell
• varcheck
• structcheck
• staticcheck
• errcheck
• unconvert
• unused

Issues Resolved

List any existing issues this pull request resolves.

Checklist

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• I have read the Contributing Guidelines.

Tests

• I have added tests to cover my changes.
• All tests pass when I run make test.

Documentation

• My change requires a change to the documentation.
• I have updated the documentation accordingly.

Code Style

• My code follows the code style of this project.