fix(bulk_load): fix remove_local_bulk_load_dir()

[zhangyifan27]

Recently our users encountered problems while using bulk_load, their job always failed, and we found remove_directory errors in replica server log:

W2021-04-22 11:15:40.633 (1619061340633182759 122434) replica.replica20.0400de080018c494: filesystem.cpp:329:remove_directory(): remove /home/work/ssd3/pegasus/c4tst-bulkload/replica/reps/46.18.pegasus/bulk_load failed, err = Directory not empty
E2021-04-22 11:15:40.633 (1619061340633219926 122434) replica.replica20.0400de080018c494: replica_bulk_loader.cpp:599:remove_local_bulk_load_dir(): [[email protected]:34801] remove bulk_load dir(/home/work/ssd3/pegasus/c4tst-bulkload/replica/reps/46.18.pegasus/bulk_load) failed

The reason is that we couldn't remove a directory using whiling writing files in this directory(see the added tests in HDFSClientTest). This patch rename unused bulkload dir to a garbage dir instead of just removing it, then remove garbage dir, disk cleaner would retry to remove it if failed.

[foreverneverer]

before starting to download bulkload

I don't see remove before starting? isn't it in this pr?

[zhangyifan27]

before starting to download bulkload

I don't see remove before starting? isn't it in this pr?

Because do_bulkload(), start_bulkload() would be executed several times during the bulkload progress, so it is not safe to remove the bulk_load_dir in the begining of any function. I edited the description.