MAGETWO-36067: Move dev/shell/indexer.php

- fixing incorrect namespace usage

app/code/Magento/Indexer/Console/Command/AbstractIndexerManageCommand.php

@@ -9,6 +9,7 @@ use Symfony\Component\Console\Input\InputInterface;
 use Symfony\Component\Console\Output\OutputInterface;
 use Symfony\Component\Console\Input\InputOption;
 use Symfony\Component\Console\Input\InputArgument;
+use Magento\Indexer\Model\IndexerInterface;
 
 /**
  * An Abstract class for all Indexer related commands.