This patch:
- add --auto-answer CLI argument option
- bind it to a new Manager atomic bool
- force a answerCall to be called if an incoming call is created and
if the autoAnswer bool is true

Note: this option is not intended to be use with a client.
Use at your own risk.

Change-Id: I7c3edbbaea5462b2dfda9ec68dd9e41667f00aca
Tuleap: #425