[PATCH 1 of 2] run-tests: convert prereq bytes to string

[timeless]

# HG changeset patch
# User timeless <timeless at mozdev.org>
# Date 1459315611 0
#      Wed Mar 30 05:26:51 2016 +0000
# Node ID d5a110d3c09a84a41c977e33f07eaa0f14003dfd
# Parent  ff0d3b6b287f89594bd8d0308fe2810d2a18ea01
run-tests: convert prereq bytes to string


Without this, run-tests would generate:
WARNING: Did not find prerequisite tool: b'python3.5'

diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -2518,7 +2518,8 @@
             if found:
                 vlog("# Found prerequisite", p, "at", found)
             else:
-                print("WARNING: Did not find prerequisite tool: %s " % p)
+                print("WARNING: Did not find prerequisite tool: %s " %
+                      p.decode("utf-8"))
 
 if __name__ == '__main__':
     runner = TestRunner()