change test to slider for disk create

app/UI/Disk/Forms/CreateForm.php

@@ -43,7 +43,6 @@ class CreateForm extends BaseForm implements ClientArea
         $this->setProvider(new DiskProvider());
         $this->initFields();
         $this->loadDataToForm();
-        $this->resourceManager = new ResourceManager();
     }
 
     public function getAllowedActions()
@@ -54,6 +53,7 @@ class CreateForm extends BaseForm implements ClientArea
     private function initFields()
     {
         //size
+        $this->resourceManager = new ResourceManager();
         $field = new Range('size', $this->configuration()->serverDiskSize->min, $this->resourceManager->disk()->free());
         $field->addValidator(new DiskSizeValidator('additionalDiskSize',true));
         $field->setDefaultValue($this->configuration()->serverDiskSize->min);