fix(tests): Protect the test_log_rpc from concurrent tests

The `nodelet` and the `plugin` were using an absolute path, which
would get clobbered by concurrent tests, which can then lead to
spurious fails. Using relative paths makes this much more stable.

libs/gl-plugin/src/node/mod.rs

@@ -230,7 +230,9 @@ impl Node for PluginNodeServer {
             // log entries are produced while we're streaming the
             // backlog out, but do we care?
             use tokio::io::{AsyncBufReadExt, BufReader};
-            let file = tokio::fs::File::open("/tmp/log").await?;
+	    // The nodelet uses its CWD, but CLN creates a network
+	    // subdirectory
+            let file = tokio::fs::File::open("../log").await?;
             let mut file = BufReader::new(file).lines();
 
             tokio::spawn(async move {