NCBC-218: Add CheckExists to IView interface

Change-Id: I2048806d3ac410c4cda237aa7354097716f90065
Reviewed-on: http://review.couchbase.org/24387
Tested-by: Saakshi Manocha <saakshi.manocha@globallogic.com>
Reviewed-by: Saakshi Manocha <saakshi.manocha@globallogic.com>