Use .elp.toml location for discovering non-buck config

Summary:
When we find a `.elp.toml` file with buck disabled, we look for alternate config in the same directory.
Actually use this location, rather than the starting path for the config process.

Reviewed By: robertoaloi

Differential Revision: D53042195

fbshipit-source-id: eca6dd52d53ebfb45d536577ef54c8834b50a1cc

crates/project_model/src/lib.rs

@@ -263,7 +263,7 @@ impl ProjectManifest {
                 let buck = elp_config.clone().buck.unwrap(); // Safe from prior line
                 return Ok((elp_config.clone(), ProjectManifest::TomlBuck(buck)));
             } else {
-                let manifest = ProjectManifest::discover_in_place(path)?;
+                let manifest = ProjectManifest::discover_in_place(elp_config.config_path())?;
                 return Ok((elp_config.clone(), manifest));
             }
         }