[VOTE] AIP-52 Automatic setup and teardown tasks

[Ash Berlin-Taylor]

Hello everyone,

I am calling for a vote on AIP-52 
https://cwiki.apache.org/confluence/display/AIRFLOW/AIP-52+Automatic+setup+and+teardown+tasks
There haven't been any notable changes to the original document, mostly just 
clairifications to the proposal.
This is my +1, and the vote will last until 10am (UTC) on Monday 16th January.
Thanks,
Ash
(To remind people what this is about, here is the example from the first dicuss 
email)
```
from airflow import DAG, task, setup, teardown

with DAG(dag_id='test'):
@setup
def create_cluster():
...
return cluster_id

@task
def load(ti):
# Example:
cluster_id = ti.xcom_pull(task_id="create_cluster")

def summarize():
...

@teardown(on_failure_fail_dagrun=False)
def teardown_cluster():
...
cluster_id = ti.xcom_pull(task_id="create_cluster")

create_cluster()
load() >> summarize()
teardown_cluster()
```