Support priv/unpriv image extraction

Optionally add back privileged extraction which can be enabled with
LUET_PRIVILEGED_EXTRACT=true

Signed-off-by: Ettore Di Giacinto <mudler@sabayon.org>

vendor/github.com/mitchellh/hashstructure/include.go

@@ -0,0 +1,15 @@
+package hashstructure
+
+// Includable is an interface that can optionally be implemented by
+// a struct. It will be called for each field in the struct to check whether
+// it should be included in the hash.
+type Includable interface {
+	HashInclude(field string, v interface{}) (bool, error)
+}
+
+// IncludableMap is an interface that can optionally be implemented by
+// a struct. It will be called when a map-type field is found to ask the
+// struct if the map item should be included in the hash.
+type IncludableMap interface {
+	HashIncludeMap(field string, k, v interface{}) (bool, error)
+}