MB-100: logging sleeps in upgrade tests

Change-Id: Ic60288277e303b7355ebd35d6a60a7536bfdcd4d
Reviewed-on: http://review.couchbase.org/24265
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>