More precise compaction time calculation

When measuring the duration of view compaction, account for
the initial step of coordinating with the updater if the
updater is running in parallel. Normally this is very fast,
but for some edge cases it can take a significant amount of
time, as it did in MB-7280 (Windows environment).

Change-Id: I666c0d418c6eeda14fee92a89dc2b599b1b48355
Reviewed-on: http://review.couchbase.org/24255
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>