Prefect: Mapped task names are not grouped on dask / bokeh

[JacksonMaxfield]

Description

A clear description of the bug
See #2813 for original context.

From the 0.12.0 release task names weren't being inferred / passed properly to the dask scheduler. That was fixed for single tasks after #2814 was merged. However after just testing out current git head it seems like mapped tasks are copied over _with_ their index in the name which results in bokeh looking like:

mapped_task [0] 1/1
mapped_task [1] 1/1
mapped_task[2] 1/1
...

Expected Behavior

What did you expect to happen instead?

Previous behavior in 0.11.0 where mapped tasks were all named the same thing and so bokeh had a single progress bar for them all.

Reproduction

A minimal example that exhibits the behavior.

from distributed import Client
from prefect import Flow, task
from prefect.engine.executors import DaskExecutor

@task
def add_one(x):
    return x + 1

with Flow("test") as flow:
    values = add_one.map(range(10))

cluster = LocalCluster()
client = Client(cluster)

print(f"Dashboard available at: {client.dashboard_link}")

flow.run(executor=DaskExecutor(address=cluster.scheduler_address))

Environment

Any additional information about your environment

prefect: current git head
dask[bag]==2.18.1
distributed==2.18.0
bokeh==2.0.2

Optionally run prefect diagnostics from the command line and paste the information here

[jcrist]

Thanks for the issue report, should be fixed by #2831.

[JacksonMaxfield]

Thanks a lot!