MXS-2572 Add basic smartrouter test

Very simple, creates 10 threads that concurrently starts making
simple INSERTs and SELECTs. The purpose is to test that the basic
router to router mechanism of smartrouter works.

maxscale-system-test/mariadb_func.h

@@ -321,6 +321,11 @@ public:
         return get_row(m_conn, q);
     }
 
+    Result rows(const std::string& q) const
+    {
+        return get_result(m_conn, q);
+    }
+
     std::string field(std::string q, int idx = 0)
     {
         Row r = get_row(m_conn, q);