Fix configurable attribute options not being sorted

See github issue #7441, internal ticket MAGETWO-61484 and PR #12420.

Author: wardcapp

app/code/Magento/ConfigurableProduct/Model/AttributeOptionProvider.php

@@ -122,6 +122,12 @@ private function getAttributeOptionsSelect(AbstractAttribute $superAttribute, $p
                 ]
             ),
             []
+        )->joinInner(
+            ['attribute_option' => $this->attributeResource->getTable('eav_attribute_option')],
+            'attribute_option.option_id = entity_value.value',
+            []
+        )->order(
+            'attribute_option.sort_order ASC'
         )->where(
             'super_attribute.product_id = ?',
             $productId

app/code/Magento/ConfigurableProduct/Test/Unit/Model/AttributeOptionProviderTest.php

@@ -97,7 +97,7 @@ protected function setUp()
             ->disableOriginalConstructor()
             ->getMockForAbstractClass();
         $this->select = $this->getMockBuilder(Select::class)
-            ->setMethods(['from', 'joinInner', 'joinLeft', 'where', 'columns'])
+            ->setMethods(['from', 'joinInner', 'joinLeft', 'where', 'columns', 'order'])
             ->disableOriginalConstructor()
             ->getMock();
         $this->connectionMock->expects($this->any())
@@ -161,10 +161,28 @@ public function testGetAttributeOptions(array $options)
 
         $this->select->expects($this->exactly(1))->method('from')->willReturnSelf();
         $this->select->expects($this->exactly(1))->method('columns')->willReturnSelf();
-        $this->select->expects($this->exactly(5))->method('joinInner')->willReturnSelf();
+        $this->select->expects($this->exactly(6))->method('joinInner')->willReturnSelf();
         $this->select->expects($this->exactly(3))->method('joinLeft')->willReturnSelf();
+        $this->select->expects($this->exactly(1))->method('order')->willReturnSelf();
         $this->select->expects($this->exactly(2))->method('where')->willReturnSelf();
 
+        $this->attributeResource->expects($this->exactly(9))
+            ->method('getTable')
+            ->will(
+                $this->returnValueMap(
+                    [
+                        ['catalog_product_super_attribute', 'catalog_product_super_attribute value'],
+                        ['catalog_product_entity', 'catalog_product_entity value'],
+                        ['catalog_product_super_link', 'catalog_product_super_link value'],
+                        ['eav_attribute', 'eav_attribute value'],
+                        ['catalog_product_entity', 'catalog_product_entity value'],
+                        ['catalog_product_super_attribute_label', 'catalog_product_super_attribute_label value'],
+                        ['eav_attribute_option', 'eav_attribute_option value'],
+                        ['eav_attribute_option_value', 'eav_attribute_option_value value']
+                    ]
+                )
+            );
+
         $this->abstractAttribute->expects($this->any())
             ->method('getBackendTable')
             ->willReturn('getBackendTable value');
@@ -193,10 +211,27 @@ public function testGetAttributeOptionsWithBackendModel(array $options)
 
         $this->select->expects($this->exactly(1))->method('from')->willReturnSelf();
         $this->select->expects($this->exactly(0))->method('columns')->willReturnSelf();
-        $this->select->expects($this->exactly(5))->method('joinInner')->willReturnSelf();
+        $this->select->expects($this->exactly(6))->method('joinInner')->willReturnSelf();
         $this->select->expects($this->exactly(1))->method('joinLeft')->willReturnSelf();
+        $this->select->expects($this->exactly(1))->method('order')->willReturnSelf();
         $this->select->expects($this->exactly(2))->method('where')->willReturnSelf();
 
+        $this->attributeResource->expects($this->exactly(7))
+            ->method('getTable')
+            ->will(
+            $this->returnValueMap(
+                [
+                    ['catalog_product_super_attribute', 'catalog_product_super_attribute value'],
+                    ['catalog_product_entity', 'catalog_product_entity value'],
+                    ['catalog_product_super_link', 'catalog_product_super_link value'],
+                    ['eav_attribute', 'eav_attribute value'],
+                    ['catalog_product_entity', 'catalog_product_entity value'],
+                    ['catalog_product_super_attribute_label', 'catalog_product_super_attribute_label value'],
+                    ['eav_attribute_option', 'eav_attribute_option value']
+                ]
+            )
+        );
+
         $source = $this->getMockBuilder(AbstractSource::class)
             ->disableOriginalConstructor()
             ->setMethods(['getOptionText'])