Fix abort error when run with driver script when foreign keys are

enabled

https://perconadev.atlassian.net/browse/PSTRESS-152

Problem
=======
The parent table pointer of the foreign key table object became invalid
after the first trial and was not updated properly for the subsequent
trials causing SIGSEGV errors.

Solution
========
The parent table name is also stored in the dll file for each step and
the parent table pointer for tables with foreign keys is set properly
when metadata is loaded from the dll files.

Author: VarunNagaraju

src/random_test.cpp

@@ -1020,8 +1020,11 @@ template <typename Writer> void Table::Serialize(Writer &writer) const {
     }
   } else if (type == FK) {
     auto fk_table = static_cast<const FK_table *>(this);
+    std::string parent = fk_table->parent->name_;
     std::string on_update = fk_table->enumToString(fk_table->on_update);
     std::string on_delete = fk_table->enumToString(fk_table->on_delete);
+    writer.String("parent");
+    writer.String(parent.c_str(), static_cast<SizeType>(parent.length()));
     writer.String("on_update");
     writer.String(on_update.c_str(), static_cast<SizeType>(on_update.length()));
     writer.String("on_delete");
@@ -3360,7 +3363,15 @@ static std::string load_metadata_from_file() {
     } else if (table_type == "FK") {
       std::string on_update = tab["on_update"].GetString();
       std::string on_delete = tab["on_delete"].GetString();
+      std::string parent_name = tab["parent"].GetString();
+
       table = new FK_table(name, on_update, on_delete);
+      for (auto &tbl : *all_tables) {
+        if (tbl->name_ == parent_name) {
+            static_cast<FK_table *>(table)->parent = tbl;
+            break;
+        }
+      }
     } else
       throw std::runtime_error("Unhandle Table type " + table_type);