sweet: require heap profiles to be available in cockroach benchmark

Currently the cockroachdb benchmark is failing in TestSweetEndToEnd
because CPU profiling fails (and thus PGO-based builds fail). Fix this
by requiring that some profile be obtainable for each instance before
starting the benchmark properly. I suspect there is an internal race,
wherein even if the server is up and running by some metric, CPU
profiles aren't yet ready.

For #56958.

Change-Id: I4c907b4394f249f3f1cac6768e641fafda20f511
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/614536
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

sweet/benchmarks/cockroachdb/main.go

diff --git a/sweet/benchmarks/cockroachdb/main.go b/sweet/benchmarks/cockroachdb/main.go
index 0d0979c..ea620e2 100644
--- a/sweet/benchmarks/cockroachdb/main.go
+++ b/sweet/benchmarks/cockroachdb/main.go
@@ -13,6 +13,7 @@
 	"flag"
 	"fmt"
 	"log"
+	"net/http"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -255,6 +256,15 @@
 	if err := cmd.Run(); err != nil {
 		return err
 	}
+	// Check to see if profiling works. We don't care what the data is, we just want to
+	// make sure that it doesn't fail. We've unfortunately seen this fail before.
+	// See #56958.
+	endpoint := fmt.Sprintf("http://%s:%d/%s", cfg.host, i.httpPort, diagnostics.MemProfile.HTTPEndpoint())
+	resp, err := http.Get(endpoint)
+	if err != nil {
+		return err
+	}
+	resp.Body.Close()
 	return nil
 }