buildman: Add a space before the list of boards

Tweak the output slightly so we don't get things like:

   - board1 board2+  board3 board4

There should be a space before the '+'.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/builder.py b/tools/buildman/builder.py
index 1b0ad99..54f3292 100644
--- a/tools/buildman/builder.py
+++ b/tools/buildman/builder.py
@@ -664,7 +664,7 @@
                 arch = 'unknown'
             str = self.col.Color(color, ' ' + target)
             if not arch in done_arch:
-                str = self.col.Color(color, char) + '  ' + str
+                str = ' %s  %s' % (self.col.Color(color, char), str)
                 done_arch[arch] = True
             if not arch in arch_list:
                 arch_list[arch] = str