sweet/benchmarks/etcd: don't build on Plan 9

This package has no relevance for Plan 9 and won't build because of
references to undefined symbols like syscall.UnixRights. Add a
!plan9 build tag to avoid this.

Fixes golang/go#68287

Change-Id: I4a0bb76d26f585b8e0371febb98ae0c57b84c237
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/596437
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed