MB-100: fix write and hot ratios in reb-vperf configs

Change-Id: I222edaa1a0d567c9af4e2c5c7986db2c09021b9b
Reviewed-on: http://review.couchbase.org/24379
Reviewed-by: Farshid Ghods <farshid@couchbase.com>
Tested-by: Farshid Ghods <farshid@couchbase.com>