Consul configuration support

[jerome-jutteau]

Hi,
As of today we have two way to configure Butterfly options:

1. through command line parameters
2. through configuration file

We would need to be able to tweak any option butterfly would need through Consul.
Ideally command-line option(s) to provide consul connection details would be ideal.

Note that Butterfly can just read one-time the configuration on consul and start, no need for update or hot-reloading