cbuildbot: Preserve chromite-bootstrap directory during Cleanup.

Don't delete the chromite-bootstrap directory during the Cleanup
Stage.

BUG=chromium:447353
TEST=cbuildbot local run with --test-bootstrap. Cleanup step lists
'chromite-bootstrap' as a directory to not delete.

Change-Id: If92a1dc0742dc924f36ea12b972ed966f2b6e31a
Reviewed-on: https://chromium-review.googlesource.com/239594
Trybot-Ready: Simran Basi <sbasi@chromium.org>
Tested-by: Simran Basi <sbasi@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Simran Basi <sbasi@chromium.org>
diff --git a/scripts/cbuildbot.py b/scripts/cbuildbot.py
index ebcb037..daf519e 100644
--- a/scripts/cbuildbot.py
+++ b/scripts/cbuildbot.py
@@ -1829,7 +1829,8 @@
     # https://chromium-review.googlesource.com/25359
     # is landed- it's sensitive to the manifest-versions cache path.
     options.preserve_paths = set(['manifest-versions', '.cache',
-                                  'manifest-versions-internal'])
+                                  'manifest-versions-internal',
+                                  'chromite-bootstrap'])
     if log_file is not None:
       # We don't want the critical section to try to clean up the tee process,
       # so we run Tee (forked off) outside of it. This prevents a deadlock