sweet/benchmarks/tile38: wait for command success

Starting in 1.26.1
Tile38 accepts connections before it is fully ready for data processing.
All commands return an error other than OUTPUT, PING, and ECHO until the
server is fully ready.

We need the server to be fully ready before starting the benchmark, so
add a check that a dummy command works before declaring the server

Our benchmark is still using 1.25.3, but this future-proofs us for when
we do upgrade.

For golang/go#53081.

Change-Id: I0f48196d105d90f3f8440871aa481192cb515bf1
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/409794
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
1 file changed