MB-100: increase minimum # of clients for load phase

Change-Id: I5567f33ab4991dfd8ffa970ac5ff42dd40ed79c8
Reviewed-on: http://review.couchbase.org/25186
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>