Set config file path via PFTQCONFIG env var

[ordovicia]

With this PR merged, pftaskqueue will read PFTQ_CONFIG environment variable (if set) to get the path of a config file.
--config flag is prioritized over PFTQ_CONFIG env var, so this change should not break the current behavior.

This feature would be useful when one does not want to place .pftaskqueue.yaml on a home directory and does not also want to type --config=... flag every time.

[everpeace]

Thanks for the contribution!

Currently, pftskqueue support config values from envvars. This feature can load foo.bar value from PFTQ_FOO_BAR. Thus, supporting PFTQ_CONFIG for config filename might cause a conflict in the future although current configuration doesn't have config key.

If we can find different prefix, I'm ok. What do you think?

[ordovicia]

Thank you for your quick response.

I came up with three options:

1. PFTQCONFIG
2. PFTASKQ_CONFIG
3. PFTASKQUEUE_CONFIG

I am a little inclined to the option 1 because it is the most concise.
c698823 changes the environment variable name to PFTQCONFIG.

But I am fine with other names.
What name do you think is the best?

[everpeace]

I came up with three options:

• PFTQCONFIG
• PFTASKQ_CONFIG
• PFTASKQUEUE_CONFIG

I am a little inclined to the option 1 because it is the most concise.

Agreed. I also prefer to PFTQCONFIG. Thanks!!