Find mullvad packages in new cache directory

Instead of assuming that the needed app packages (mullvad installation +
GUI tests) are present inside of the test framework folder,
`test-manager` now creates a directory in `dirs::cache_dir` on the host system.

test/test-manager/src/package.rs

@@ -64,8 +64,12 @@ async fn find_app(
     let mut app = app.to_owned();
     app.make_ascii_lowercase();
 
-    // Search for package in ./packages/
-    let mut dir = fs::read_dir("./packages/")
+    let packages_dir = dirs::cache_dir()
+        .context("Could not find cache directory")?
+        .join("mullvad-test")
+        .join("packages");
+    fs::create_dir_all(&packages_dir).await?;
+    let mut dir = fs::read_dir(packages_dir)
         .await
         .context("Failed to list packages")?;