Use consistent approach when try to query super-read-only

[rsajwani]

We have been using two approaches while querying for super-read-only in our code base.

1- SELECT @@global.super_read_only
2- SHOW VARIABLES LIKE 'super_read_only'

Same for read-only attribute
1- SELECT @@global.read_only
2- SHOW VARIABLES LIKE 'read_only'

i think we should be consistent in our approach. The option#1 looks better.. .

[deepthi]

Just a note that everything should be going through the flavor interface as well. I hope we are not hardcoding either of these two usages in random places.