pageserver: allow for unit test stress test (#11112)

## Problem

I like using `cargo stress` to hammer on a test, but it doesn't work out
of the box because it does parallel runs by default and tests always use
the same repo dir.

## Summary of changes

Add an uuid to the test repo dir when generating it.

Cargo.lock

@@ -4303,6 +4303,7 @@ dependencies = [
  "tracing",
  "url",
  "utils",
+ "uuid",
  "wal_decoder",
  "walkdir",
  "workspace_hack",

pageserver/Cargo.toml

@@ -98,6 +98,7 @@ criterion.workspace = true
 hex-literal.workspace = true
 tokio = { workspace = true, features = ["process", "sync", "fs", "rt", "io-util", "time", "test-util"] }
 indoc.workspace = true
+uuid.workspace = true
 
 [[bench]]
 name = "bench_layer_map"

pageserver/src/config.rs

@@ -491,7 +491,9 @@ impl PageServerConf {
     #[cfg(test)]
     pub fn test_repo_dir(test_name: &str) -> Utf8PathBuf {
         let test_output_dir = std::env::var("TEST_OUTPUT").unwrap_or("../tmp_check".into());
-        Utf8PathBuf::from(format!("{test_output_dir}/test_{test_name}"))
+
+        let test_id = uuid::Uuid::new_v4();
+        Utf8PathBuf::from(format!("{test_output_dir}/test_{test_name}_{test_id}"))
     }
 
     pub fn dummy_conf(repo_dir: Utf8PathBuf) -> Self {