Used `go fmt` rules to migrate away from deprecated functions, for
instance `gofmt -w -s -r 'ioutil.TempDir(a, b) -> os.MkdirTemp(a, b)'`
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>
`github.com/pkg/errors` is deprecated since quite some time so we now
use the native error wrapping for more idiomatic golang.
Signed-off-by: Sascha Grunert <sgrunert@redhat.com>