buildman: Avoid using board as a variable

We have a module called 'board'. Sometimes buildman uses 'brd' as an
instance variable but sometimes it uses 'board', which is confusing and
can mess with the module handling. Update the code to use 'brd'
consistently, making it easier for tools to determine when the module
is being referenced.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/test.py b/tools/buildman/test.py
index 2728743..62ad25d 100644
--- a/tools/buildman/test.py
+++ b/tools/buildman/test.py
@@ -184,8 +184,8 @@
         # TODO(sjg@chromium.org): If plus is '', we shouldn't need this
         expect += ' ' + col.build(expected_colour, plus)
         expect += '  '
-        for board in boards:
-            expect += col.build(expected_colour, ' %s' % board)
+        for brd in boards:
+            expect += col.build(expected_colour, ' %s' % brd)
         self.assertEqual(text, expect)
 
     def _SetupTest(self, echo_lines=False, threads=1, **kwdisplay_args):