Calculate average for p99 and p95 and compare to the criteria

Change-Id: I2f48fae913a1db6d86f4173c89b3a80bb6da848e
Reviewed-on: http://review.couchbase.org/37157
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Li Yang <lichenyang2@gmail.com>