VOL-1460 Updated core to use voltha-protos instead of local protos
Moved protos to python directory in order to maintain functionaly of containers built there.
Added capability to do local builds of protos
Added instructions on running dep ensure for getting protos.
Updated github.com/golang/protobuf version to v1.3.1

Change-Id: Ia6ef55f07f0d5dcb5b750d7c37b21b71db85bfc4
diff --git a/vendor/github.com/golang/protobuf/proto/extensions.go b/vendor/github.com/golang/protobuf/proto/extensions.go
index 816a3b9..fa88add 100644
--- a/vendor/github.com/golang/protobuf/proto/extensions.go
+++ b/vendor/github.com/golang/protobuf/proto/extensions.go
@@ -185,9 +185,25 @@
 	// extension will have only enc set. When such an extension is
 	// accessed using GetExtension (or GetExtensions) desc and value
 	// will be set.
-	desc  *ExtensionDesc
+	desc *ExtensionDesc
+
+	// value is a concrete value for the extension field. Let the type of
+	// desc.ExtensionType be the "API type" and the type of Extension.value
+	// be the "storage type". The API type and storage type are the same except:
+	//	* For scalars (except []byte), the API type uses *T,
+	//	while the storage type uses T.
+	//	* For repeated fields, the API type uses []T, while the storage type
+	//	uses *[]T.
+	//
+	// The reason for the divergence is so that the storage type more naturally
+	// matches what is expected of when retrieving the values through the
+	// protobuf reflection APIs.
+	//
+	// The value may only be populated if desc is also populated.
 	value interface{}
-	enc   []byte
+
+	// enc is the raw bytes for the extension field.
+	enc []byte
 }
 
 // SetRawExtension is for testing only.
@@ -334,7 +350,7 @@
 			// descriptors with the same field number.
 			return nil, errors.New("proto: descriptor conflict")
 		}
-		return e.value, nil
+		return extensionAsLegacyType(e.value), nil
 	}
 
 	if extension.ExtensionType == nil {
@@ -349,11 +365,11 @@
 
 	// Remember the decoded version and drop the encoded version.
 	// That way it is safe to mutate what we return.
-	e.value = v
+	e.value = extensionAsStorageType(v)
 	e.desc = extension
 	e.enc = nil
 	emap[extension.Field] = e
-	return e.value, nil
+	return extensionAsLegacyType(e.value), nil
 }
 
 // defaultExtensionValue returns the default value for extension.
@@ -488,7 +504,7 @@
 	}
 	typ := reflect.TypeOf(extension.ExtensionType)
 	if typ != reflect.TypeOf(value) {
-		return errors.New("proto: bad extension value type")
+		return fmt.Errorf("proto: bad extension value type. got: %T, want: %T", value, extension.ExtensionType)
 	}
 	// nil extension values need to be caught early, because the
 	// encoder can't distinguish an ErrNil due to a nil extension
@@ -500,7 +516,7 @@
 	}
 
 	extmap := epb.extensionsWrite()
-	extmap[extension.Field] = Extension{desc: extension, value: value}
+	extmap[extension.Field] = Extension{desc: extension, value: extensionAsStorageType(value)}
 	return nil
 }
 
@@ -541,3 +557,51 @@
 func RegisteredExtensions(pb Message) map[int32]*ExtensionDesc {
 	return extensionMaps[reflect.TypeOf(pb).Elem()]
 }
+
+// extensionAsLegacyType converts an value in the storage type as the API type.
+// See Extension.value.
+func extensionAsLegacyType(v interface{}) interface{} {
+	switch rv := reflect.ValueOf(v); rv.Kind() {
+	case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
+		// Represent primitive types as a pointer to the value.
+		rv2 := reflect.New(rv.Type())
+		rv2.Elem().Set(rv)
+		v = rv2.Interface()
+	case reflect.Ptr:
+		// Represent slice types as the value itself.
+		switch rv.Type().Elem().Kind() {
+		case reflect.Slice:
+			if rv.IsNil() {
+				v = reflect.Zero(rv.Type().Elem()).Interface()
+			} else {
+				v = rv.Elem().Interface()
+			}
+		}
+	}
+	return v
+}
+
+// extensionAsStorageType converts an value in the API type as the storage type.
+// See Extension.value.
+func extensionAsStorageType(v interface{}) interface{} {
+	switch rv := reflect.ValueOf(v); rv.Kind() {
+	case reflect.Ptr:
+		// Represent slice types as the value itself.
+		switch rv.Type().Elem().Kind() {
+		case reflect.Bool, reflect.Int32, reflect.Int64, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String:
+			if rv.IsNil() {
+				v = reflect.Zero(rv.Type().Elem()).Interface()
+			} else {
+				v = rv.Elem().Interface()
+			}
+		}
+	case reflect.Slice:
+		// Represent slice types as a pointer to the value.
+		if rv.Type().Elem().Kind() != reflect.Uint8 {
+			rv2 := reflect.New(rv.Type())
+			rv2.Elem().Set(rv)
+			v = rv2.Interface()
+		}
+	}
+	return v
+}