MAGETWO-47451: 'in' filter does not work in list APIs

- added conversion from string to array for 'in' and 'nin' in Mysql Adapter

Author: arkadiych

lib/internal/Magento/Framework/DB/Adapter/Pdo/Mysql.php

@@ -2789,6 +2789,9 @@ public function prepareSqlCondition($fieldName, $condition)
                 if (($key == 'seq') || ($key == 'sneq')) {
                     $key = $this->_transformStringSqlCondition($key, $value);
                 }
+                if (($key == 'in' || $key == 'nin') && is_string($value)) {
+                    $value = explode(',', $value);
+                }
                 $query = $this->_prepareQuotedSqlCondition($conditionKeyMap[$key], $value, $fieldName);
             } else {
                 $queries = [];