buildman: Use spaces in the board list

At present the board names shown with -l are separated by commas. This
makes it hard to double-click to select a particular board. Also it is not
possible to select all boards and paste them as arguments to a subsequent
buildman run, since buildman requires spaces to separate the list on the
command line, not commas.

Change the output format to use spaces instead of commas.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/test.py b/tools/buildman/test.py
index a64372d..a495df0 100644
--- a/tools/buildman/test.py
+++ b/tools/buildman/test.py
@@ -249,9 +249,9 @@
                 new_lines.append(expect)
             return '\n'.join(new_lines)
 
-        boards1234 = 'board1,board2,board3,board4' if list_error_boards else ''
-        boards234 = 'board2,board3,board4' if list_error_boards else ''
-        boards34 = 'board3,board4' if list_error_boards else ''
+        boards1234 = 'board1 board2 board3 board4' if list_error_boards else ''
+        boards234 = 'board2 board3 board4' if list_error_boards else ''
+        boards34 = 'board3 board4' if list_error_boards else ''
         boards4 = 'board4' if list_error_boards else ''
 
         # Upstream commit: no errors