Fix to bug #557, http://bugs.mariadb.com/show_bug.cgi?id=557
query_classifier.cc: added function for printing combined query type from a bit field.
query_classifier.h: identify query types SHOW DATABASE, and SHOW TABLES to make log entries more understandable.
mysql_common.c: moved some trace log commands to debug log.
readwritesplit.c: moved some trace logs to debug log, added trace log commands to gather routing, query type and session information to one log entry.
skygw_debug.h: added string macros for several query and hint types.