Remove dependency on skygw_utils.h

- STRERROR_BUFLEN moved to cdefs.h and renamed to MXS_STRERROR_BUFLEN.
  Better would be to provide a 'const char* mxs_strerror(int errno)'
  that would have a thread specific buffer for the error message.
- MIN and MAX also moved to defs.h as MXS_MIN and MXS_MAX.
- Now only mlist.h of the headers depend upon skygw_utils.h.

server/modules/protocol/MySQL/mysql_common.c

@@ -844,7 +844,7 @@ void init_response_status(GWBUF*             buf,
             nparam = gw_mysql_get_byte2(readbuf);
             gwbuf_copy_data(buf, 11, 2, readbuf);
             nattr = gw_mysql_get_byte2(readbuf);
-            *npackets = 1 + nparam + MIN(1, nparam) + nattr + MIN(nattr, 1);
+            *npackets = 1 + nparam + MXS_MIN(1, nparam) + nattr + MXS_MIN(nattr, 1);
             break;
 
         case MYSQL_COM_QUIT: