Makefile: run tests with PYTHONHASHSEED=random

This will make it harder to check in tests that have dependencies on
Python's default hash ordering.

Change-Id: Id9ddba57b2f3a489d28605443510bbebc198c921

Makefile

@@ -8,7 +8,7 @@ TESTRUNNER ?= unittest
 else
 TESTRUNNER ?= unittest2.__main__
 endif
-RUNTEST = PYTHONPATH=.:$(PYTHONPATH) $(PYTHON) -m $(TESTRUNNER)
+RUNTEST = PYTHONHASHSEED=random PYTHONPATH=.:$(PYTHONPATH) $(PYTHON) -m $(TESTRUNNER)
 
 DESTDIR=/