make test: fix logging

Change-Id: I3867d50746f0f424c8e94929171363e5b2e4d470
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/test/framework.py b/test/framework.py
index 2a2dfd4..9151fa5 100644
--- a/test/framework.py
+++ b/test/framework.py
@@ -532,7 +532,7 @@
             stderr_log(single_line_delim)
             stderr_log('VPP output to stderr while running %s:', cls.__name__)
             stderr_log(single_line_delim)
-            vpp_output = "".join(str(cls.vpp_stderr_deque))
+            vpp_output = "".join(cls.vpp_stderr_deque)
             with open(cls.tempdir + '/vpp_stderr.txt', 'w') as f:
                 f.write(vpp_output)
             stderr_log('\n%s', vpp_output)