Reverse setBallotInProg parameter meaning.

To reflect the name better.

Change-Id: I814b77097f52aff65d668bd43f2fc23ae998c97e
Reviewed-on: http://review.couchbase.org/42943
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>