Differentiate between ignored testPackages and ignored coverPackages

[f-blass]

In my project setup I have test packages like api_test which contain only tests for the package api. I want to execute these but I do not want to have coverage for the api_test package.
Furthermore I have a package test with test helpers functions. Tests from here could be executed, but yet again I do not want to include coverage data for this package.

With the --ignore flag packages are both excluded from the go test <packages> command, as well as the -coverpkg=<packages> option.

The ..._test package construct is common in Go, so I think it would be helpful to have different ignores for testPackages and coverPackages.