containerd: include zfs plugin by default

Signed-off-by: Stephen J Day <stephen.day@docker.com>

vendor/github.com/mistifyio/go-zfs/error.go

@@ -0,0 +1,18 @@
+package zfs
+
+import (
+	"fmt"
+)
+
+// Error is an error which is returned when the `zfs` or `zpool` shell
+// commands return with a non-zero exit code.
+type Error struct {
+	Err    error
+	Debug  string
+	Stderr string
+}
+
+// Error returns the string representation of an Error.
+func (e Error) Error() string {
+	return fmt.Sprintf("%s: %q => %s", e.Err, e.Debug, e.Stderr)
+}