[AIRFLOW-6686] Fix syntax error constructing list of process ids (#7298)
[AIRFLOW-6686] Fix syntax error constructing list of process ids (#7298)

Construction of list of pids passed in kill command raises a Syntax error because
ordering of the arguments to `map` function doesn't conform to function
parameter definition.

A list comprehension replaces the existing `map` function to make the code
forward compatible with Python 3 and at the same time expand to a list of pids.

(cherry picked from commit d1cedc4f691e683bf1ed54aee3a2c1a54013bbb3)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow