Handle callback from Jira oAuth 2-legged in webserver thread

[mafrosis]

The current auth flow looks like the following, with a manual visit to the generated URL in your browser before returning to enter y.

> docker-compose run --rm -v ~/jiracli.pem:/tmp/pk:ro jiracli clone --oauth-private-key=/tmp/pk http://locke:8666/TEST
Cloning project TEST from http://locke:8666

Please visit this URL to authorize jiracli to access your data:
    http://locke:8666/plugins/servlet/oauth/authorize?oauth_token=XYG9sOoNjXnOXUCS16VWpfY9Vei7qIPe

Have you authorized this program to connect on your behalf to http://locke:8666? [y/N]: y
Authenticated with http://locke:8666
...

It's possible to configure the Jira oAuth app with a callback, and then run a webserver thread in jiracli to remove the need to enter y.