Allow parameters in store URIs

This is to allow store-specific configuration,
e.g. s3://my-cache?compression=bzip2&secret-key=/path/to/key.

src/libstore/remote-store.cc

@@ -49,6 +49,12 @@ RemoteStore::RemoteStore(size_t maxConnections)
 }
 
 
+std::string RemoteStore::getUri()
+{
+    return "daemon";
+}
+
+
 ref<RemoteStore::Connection> RemoteStore::openConnection()
 {
     auto conn = make_ref<Connection>();