Client.retire_workers(..., close_workers=False) still closes workers

Replace scheduler_ip with your scheduler IP.
Start a scheduler, and a worker connected to the scheduler.
After executing the following code, all workers are closed.

```
from dask.distributed import Client
import time

def dummy_loop(job_data):
time.sleep(20)
return True

def submit_job(scheduler_ip):
client = Client(scheduler_ip)
job_data_list = list()
for i in range(3):
job_data_list.append(1)
p = client.map(dummy_loop, job_data_list)
client.close()

def kill_job(scheduler_ip):
client = Client(scheduler_ip)

if True:
worker_status = client.scheduler_info()['workers']
worker_list = list()
for worker, status in worker_status.items():
worker_list.append(worker)

client.retire_workers(worker_list, close_workers=False)
print(client.scheduler_info()['workers'])

client.close()

def do_main():
scheduler_ip = '10.0.0.2:8786'
submit_job(scheduler_ip)
kill_job(scheduler_ip)

if __name__ == '__main__':
do_main()

```