libpod/runtime: switch to golang native error wrapping

We now use the golang error wrapping format specifier `%w` instead of
the deprecated github.com/pkg/errors package.

[NO NEW TESTS NEEDED]

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

pkg/errorhandling/errorhandling_test.go

@@ -0,0 +1,53 @@
+package errorhandling
+
+import (
+	"errors"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCause(t *testing.T) {
+	t.Parallel()
+
+	for _, tc := range []struct {
+		name        string
+		err         func() error
+		expectedErr error
+	}{
+		{
+			name:        "nil error",
+			err:         func() error { return nil },
+			expectedErr: nil,
+		},
+		{
+			name:        "equal errors",
+			err:         func() error { return errors.New("foo") },
+			expectedErr: errors.New("foo"),
+		},
+		{
+			name:        "wrapped error",
+			err:         func() error { return fmt.Errorf("baz: %w", fmt.Errorf("bar: %w", errors.New("foo"))) },
+			expectedErr: errors.New("foo"),
+		},
+		{
+			name: "max depth reached",
+			err: func() error {
+				err := errors.New("error")
+				for i := 0; i <= 101; i++ {
+					err = fmt.Errorf("%d: %w", i, err)
+				}
+				return err
+			},
+			expectedErr: fmt.Errorf("0: %w", errors.New("error")),
+		},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			err := Cause(tc.err())
+			assert.Equal(t, tc.expectedErr, err)
+		})
+	}
+}