GNU Radio 3.8 support

https://wiki.gnuradio.org/index.php/GNU_Radio_3.8_OOT_Module_Porting_Guide

Change-Id: I23dd638c8c48ed0a4b50559ce33fbd5e60b7dcbc
diff --git a/python/qa_burst_printer.py b/python/qa_burst_printer.py
index a3d50d5..c1fdfaf 100755
--- a/python/qa_burst_printer.py
+++ b/python/qa_burst_printer.py
@@ -52,7 +52,7 @@
         out = ""
         for l in expected_lines:
             out = out + l + "\n"
-        return out
+        return out.encode('utf-8')
 
     def test_001_complete_bursts_prefix (self):
         """