bisect-kit: Fix template repository recreation logic

1. Recreate the repository if it doesn't exist.
2. Wait btrfs subvolumn to be deleted when calling 'btrfs subvolumn
   delete'

BUG=b:332352438
TEST=setup_cros_bisect.py sync && run_formatters.sh && run_test.sh

Change-Id: I92f4a4c185ae1c70367ab798a5f59b07d45f5afe
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/bisect-kit/+/5411071
Reviewed-by: Zheng-Jie Chang <zjchang@chromium.org>
Tested-by: Cheng-Yu Lee <cylee@google.com>
Commit-Queue: Cheng-Yu Lee <cylee@google.com>
2 files changed