Simplify setBallotInProg.

Change-Id: Ide637e24267cd654134f3b4ff0a6d946f3f86e60
Reviewed-on: http://review.couchbase.org/42944
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>