buildman: Print a message indicating the build is starting

Make it clear when buildman actually starts building. This happens when it
has prepared the threads, working directory and output directories.

Signed-off-by: Simon Glass <sjg@chromium.org>

tools/buildman/builder.py

@@ -1430,6 +1430,7 @@ class Builder:
         self._PrepareWorkingSpace(min(self.num_threads, len(board_selected)),
                 commits is not None)
         self._PrepareOutputSpace()
+        Print('\rStarting build...', newline=False)
         self.SetupBuild(board_selected, commits)
         self.ProcessResult(None)