MXS-938: Recognize transaction start

Now more information about a transaction start is provided. When
a transaction start statement is parsed, the type of the statement
with be QUERY_TYPE_BEGIN_TRX anded with QUERY_TYPE_READ or
QUERY_TYPE_WRITE if the transaction was explicitly started as READ
ONLY or READ WRITE.

Now also BEGIN WORK and [COMMIT|ROLLBACK] WORK are recognized.
"AND CHAIN" will still need to be recognized.

query_classifier/qc_mysqlembedded/qc_mysqlembedded.cc

@@ -630,6 +630,14 @@ static uint32_t resolve_query_type(THD* thd)
 
     case SQLCOM_BEGIN:
         type |= QUERY_TYPE_BEGIN_TRX;
+        if (lex->start_transaction_opt & MYSQL_START_TRANS_OPT_READ_WRITE)
+        {
+            type |= QUERY_TYPE_WRITE;
+        }
+        else if (lex->start_transaction_opt & MYSQL_START_TRANS_OPT_READ_ONLY)
+        {
+            type |= QUERY_TYPE_READ;
+        }
         goto return_qtype;
         break;