Sub-command to generate the default config

[dimberman]

Ticket was created 02/Feb/17 20:12

Description

1. Currently airflow autogenerates a default $AIRFLOW_HOME/airflow.cfg as soon as any command is issued or even when running import airflow from python, which IMO is rather intrusive (even more so when AIRFLOW_HOME defaults to the user's home directory).
2. Moreover, once the file is created it is not trivial to generate a default config again; one has to either move the existing one to another location or change (at least temporarily) AIRFLOW_HOME.

Both issues can be addressed with the extension of the CLI with a subcommand to generate the default config explicitly at will instead of implicitly at import time.

Use case / motivation

Related Issues

Moved here from https://issues.apache.org/jira/browse/AIRFLOW-833