buildman: Don't remove entire output directory when testing

When running tests the output directory is often wiped. This is only safe if
a branch is being built. The output directory may contain other things
besides the buildman test output.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 747c80d..2249b0f 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -215,7 +215,8 @@
         # output directory itself rather than any subdirectory.
         if not options.no_subdirs:
             output_dir = os.path.join(options.output_dir, dirname)
-    if clean_dir and os.path.exists(output_dir):
+    if (clean_dir and output_dir != options.output_dir and
+            os.path.exists(output_dir)):
         shutil.rmtree(output_dir)
     builder = Builder(toolchains, output_dir, options.git_dir,
             options.threads, options.jobs, gnu_make=gnu_make, checkout=True,