etcd: Replace deprecated --debug option

... to resolve the following warning.

[WARNING] Deprecated '--debug' flag is set to true (use
'--log-level=debug' instead

Change-Id: Idb412cea64dfc42e3d1223b77f134804eeb7bd60
diff --git a/lib/etcd3 b/lib/etcd3
index 4f3a7a4..0d22de8 100644
--- a/lib/etcd3
+++ b/lib/etcd3
@@ -51,7 +51,7 @@
     fi
     cmd+=" --listen-client-urls http://$SERVICE_HOST:$ETCD_PORT"
     if [ "$ENABLE_DEBUG_LOG_LEVEL" == "True" ]; then
-        cmd+=" --debug"
+        cmd+=" --log-level=debug"
     fi
 
     local unitfile="$SYSTEMD_DIR/$ETCD_SYSTEMD_SERVICE"