golangci-lint: update golangci rules and fix the lints

[cpanato]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

golangci-lint: update golangci rules and fix the lints

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes: #258

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

NONE

[cpanato]

/assign @timoreimann @prksu @MorrisLaw

[cpanato]

/test ls

[k8s-ci-robot]

@cpanato: The specified target(s) for /test were not found.
The following commands are available to trigger required jobs:

• /test pull-cluster-api-provider-digitalocean-test
• /test pull-cluster-api-provider-digitalocean-build
• /test pull-cluster-api-provider-digitalocean-verify
• /test pull-cluster-api-provider-digitalocean-lint
• /test pull-cluster-api-provider-digitalocean-e2e

The following commands are available to trigger optional jobs:

• /test pull-cluster-api-provider-digitalocean-capi-e2e
• /test pull-cluster-api-provider-digitalocean-conformance

Use /test all to run the following jobs that were automatically triggered:

• pull-cluster-api-provider-digitalocean-test
• pull-cluster-api-provider-digitalocean-build
• pull-cluster-api-provider-digitalocean-verify
• pull-cluster-api-provider-digitalocean-lint
• pull-cluster-api-provider-digitalocean-e2e

In response to this:

/test ls

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[cpanato]

/test pull-cluster-api-provider-digitalocean-capi-e2e
/test pull-cluster-api-provider-digitalocean-conformance

[timoreimann]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cpanato, timoreimann

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• OWNERS [cpanato,timoreimann]

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