tests: Prefer development Python files over installed ones.

A developer may have Open vSwitch installed, in which case many of
the Python files which are tested will be in both the development
tree and the system Python library.  When running unit tests, we
want to test the development tree, so it's better to prefer
importing those files.

Signed-off-by: Ethan Jackson <ethan@nicira.com>

Author: ejj

tests/atlocal.in

@@ -4,7 +4,7 @@ HAVE_PYTHON='@HAVE_PYTHON@'
 PERL='@PERL@'
 PYTHON='@PYTHON@'
 
-PYTHONPATH=$PYTHONPATH:$abs_top_srcdir/python:$abs_top_builddir/tests
+PYTHONPATH=$abs_top_srcdir/python:$abs_top_builddir/tests:$PYTHONPATH
 export PYTHONPATH
 
 PYTHONIOENCODING=utf_8