Make the Connector more MaxScale friendly

Currently few catalog function calls result in error, if MaxScale stands in front of servers with default settings. The solution is to set use_sql_variables_in=master in the the readwritesplit service.
Another possible solution(besides complete rewriting of the functions to make the queries they send be "good" for maxscale), is to add to the queries maxscale hints, i.e. the comment with the text /* maxscale route to master */, that will cause the same effect as use_sql_variables_in=master But hintfilter should be turned on in MaxScale, and that is not the case by default