Add driver mode interface

Implement driver mode interface for share driver, that will allow operator
to switch share drivers to work in specific mode, like single or multi SVM.

Add usage of driver mode interface to Generic driver as an example.

To set driver mode use config option 'share_driver_mode'. Available values
are specified within its help message.

Partially Implements bp driver-modes
Change-Id: I2744cccfbe2c09c3d942822f902793493cd9befb