sweet: remove etcd benchmark output spew

This causes the upstream log to be truncated, and it looks like
benchmark results are now missing for some benchmarks on some commits.

Change-Id: I29f434870a21d4ccdd0dad7d8825e5bb0fc4dbdc
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/493920
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/sweet/benchmarks/etcd/main.go b/sweet/benchmarks/etcd/main.go
index a0e1045..e82e176 100644
--- a/sweet/benchmarks/etcd/main.go
+++ b/sweet/benchmarks/etcd/main.go
@@ -322,7 +322,7 @@
 					fmt.Fprintf(os.Stderr, "failed to shutdown %s: %v", inst.name, r)
 				}
 			}
-			if inst.output.Len() != 0 {
+			if err != nil && inst.output.Len() != 0 {
 				fmt.Fprintf(os.Stderr, "=== Instance %q stdout+stderr ===\n", inst.name)
 				fmt.Fprintln(os.Stderr, inst.output.String())
 			}