MXS-2431 Recognize the XA keyword

Recognize the XA keyword and classify the statement as write.
Needs to be dealt with explicitly as sqlite3 assumes there are
no keywords starting with the letter X.

query_classifier/qc_sqlite/sqlite-src-3110100/tool/mkkeywordhash.c

@@ -500,6 +500,7 @@ static Keyword aKeywordTable[] = {
 #ifdef MAXSCALE
   { "WORK",             "TK_WORK",         ALWAYS                 },
   { "WRITE",            "TK_WRITE",        ALWAYS                 },
+  { "XA",               "TK_XA",           ALWAYS                 },
 #endif
   { "ZEROFILL",         "TK_ZEROFILL",     ALWAYS                 },
 };