etcd: enable optional log file for embedded etcd log output

In this commit we add an extra config for enabling logging to an
external file when using embedded etcd. This can be useful when running
integration tests to see more details about etcd related issues.

kvdb/etcd/embed.go

@@ -60,8 +60,8 @@ func getFreePort() int {
 // NewEmbeddedEtcdInstance creates an embedded etcd instance for testing,
 // listening on random open ports. Returns the backend config and a cleanup
 // func that will stop the etcd instance.
-func NewEmbeddedEtcdInstance(path string, clientPort, peerPort uint16) (
-	*Config, func(), error) {
+func NewEmbeddedEtcdInstance(path string, clientPort, peerPort uint16,
+	logFile string) (*Config, func(), error) {
 
 	cfg := embed.NewConfig()
 	cfg.Dir = path
@@ -70,7 +70,12 @@ func NewEmbeddedEtcdInstance(path string, clientPort, peerPort uint16) (
 	cfg.MaxTxnOps = 8192
 	cfg.MaxRequestBytes = 16384 * 1024
 	cfg.Logger = "zap"
-	cfg.LogLevel = "error"
+	if logFile != "" {
+		cfg.LogLevel = "info"
+		cfg.LogOutputs = []string{logFile}
+	} else {
+		cfg.LogLevel = "error"
+	}
 
 	// Listen on random free ports if no ports were specified.
 	if clientPort == 0 {