Expose setting to control timeout for long running index scans

There is a need to expose setting for controlling timeout for index scan. Currently there is a limit of 2 minutes for scan to finish, which is resulting to timeout issues as described in defect - MB-15645
Ideally the customer should be able to control the timeout settings for complex data sets or large numbers of scans running in parallel which lead to slower boxes. It would be very difficult to change setting at customer locations.