buildman: Add an option to flatten output directory trees

When building current source for a single board, buildman puts the output
in <output_dir>/current/current/<board>. Add an option to make it use
<output_dir>/<board> instead. This removes the unnecessary directories
in that case, controlled by the --no-subdirs/-N option.

Suggested-by: Tom Rini <trini@ti.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/test.py b/tools/buildman/test.py
index f16d2fd..c085d2f 100644
--- a/tools/buildman/test.py
+++ b/tools/buildman/test.py
@@ -373,5 +373,13 @@
         build.commit_count = 0
         self.CheckDirs(build, '/current')
 
+    def testOutputDirNoSubdirs(self):
+        build = builder.Builder(self.toolchains, BASE_DIR, None, 1, 2,
+                                checkout=False, show_unknown=False,
+                                no_subdirs=True)
+        build.commits = None
+        build.commit_count = 0
+        self.CheckDirs(build, '')
+
 if __name__ == "__main__":
     unittest.main()