run-tests: introduce a name for os.environb

On python 2 this is just os.environ, but on python 3 we need to get to
os.environb in several places.

tests/run-tests.py

@@ -66,6 +66,8 b' except ImportError:'
 from xml.dom import minidom
 import unittest
 
+osenvironb = getattr(os, 'environb', os.environ)
+
 try:
     import json
 except ImportError: