Fix bug in iperf client over adb.

This CL fixes a bug that occurs when iperf clients over adb timeout.

Test: Done
Bug: None

Change-Id: I3cb3cba4ed62a78e9ecfbc727986a5e9ccf0191d
Signed-off-by: Omar El Ayach <oelayach@google.com>
diff --git a/acts/framework/acts/controllers/iperf_client.py b/acts/framework/acts/controllers/iperf_client.py
index f6ec3f4..6993925 100644
--- a/acts/framework/acts/controllers/iperf_client.py
+++ b/acts/framework/acts/controllers/iperf_client.py
@@ -259,6 +259,7 @@
         Returns:
             The iperf result file path.
         """
+        clean_out = ''
         try:
             if not iperf_binary:
                 logging.debug('No iperf3 binary specified.  '