database/sql: do not bypass the driver locks with Context methods
When context methods were initially added it was attempted to unify
behavior between drivers without Context methods and those with
Context methods to always return right away when the Context expired.
However in doing so the driver call could be executed outside of the
scope of the driver connection lock and thus bypassing thread safety.
The new behavior waits until the driver operation is complete. It then
checks to see if the context has expired and if so returns that error.