This refactors api.Handler such that the return type is a single error instead of a user-facing error, a system-facing error, and a status code. It then handles the error specially if it is an api.Errors implementation. I also updated usage accordingly throughout the two endpoint handling packages that use api.Wrap.

Essentially this reduces

code, userErr, sysErr := someCall(inf)
if userErr != nil || sysErr != nil {
 return code, userErr, sysErr
}

to

err := someCall(inf)
if err != nil {
 return err
}

and

err := tx.QueryRow("My query", args...)
if err != nil {
 return http.StatusInternalServerError, nil, err
}

to

err := tx.QueryRow("My query", args...)
if err != nil {
 return err
}

Which Traffic Control components are affected by this PR?

• Traffic Ops

What is the best way to verify this PR?

This is just a refactor; behavior should be unchanged and the existing tests should continue to pass.

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR doesn't need a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY