sensorlog: Use built-in setsid instead of standalone binary.

Standalone setsid is not available on Darwin.

MultiPart: 2/2

Change-Id: If5837e4df12333b3030ce88fecf27cbc3afe8273
diff --git a/go/src/v.io/x/sensorlog/internal/measure/sampler/sampler.go b/go/src/v.io/x/sensorlog/internal/measure/sampler/sampler.go
index bf4561f..14c11af 100644
--- a/go/src/v.io/x/sensorlog/internal/measure/sampler/sampler.go
+++ b/go/src/v.io/x/sensorlog/internal/measure/sampler/sampler.go
@@ -36,7 +36,11 @@
 func Run(ctx *context.T, samDef *sbmodel.SamplerDef, cb MeasureCallback) error {
 	var out bytes.Buffer
 	// Run sampling script using bash and capture output.
-	sh := exec.Command("setsid", "bash")
+	sh := exec.Command("bash")
+	// Setsid to create new process group, for more robust signalling.
+	sh.SysProcAttr = &syscall.SysProcAttr{
+		Setsid: true,
+	}
 	sh.Stdin = bytes.NewBufferString(samDef.Script)
 	sh.Stdout = &out
 	// TODO(ivanpi): Fail on any stderr output?