[#91] Failover enhancements

Signed-off-by: Andrey Berezin <a.berezin@yadro.com>

src/frostfs_testlib/testing/parallel.py

@@ -42,7 +42,7 @@ def parallel(
     exceptions = [future.exception() for future in futures if future.exception()]
     if exceptions:
         message = "\n".join([str(e) for e in exceptions])
-        raise RuntimeError(f"The following exceptions occured during parallel run: {message}")
+        raise RuntimeError(f"The following exceptions occured during parallel run:\n {message}")
     return futures