syncbase/featuretests: Avoid fmt.Print in the benchmark.

Using fmt.Printf in the body of the benchmark messes up the formatting
of the output lines. Instead of:
  BenchmarkPingPongPair-4       1	100004362746 ns/op
we were getting:
  BenchmarkPingPongPair-4	Iteration 0 of 1
  Avg Time from 0 to 1: 129228293 ns
  Avg Time from 1 to 0: 70780430 ns
  Avg Time per iteration: 200008724 ns
         1	100004362746 ns/op

The latter isn't parseable by golang.org/x/tools/benchmark/parse
which prevents the numbers from this benchmark from being uploaded
to the benchmark archival servers.

Change-Id: If3739f636850487860308b5a68f6912eca5365eb
1 file changed