Stop writing an empty config file

[macmv]

Ticket(s): ENG-6776

Right now, we do the following in fauna project init:

• Write an empty config file
• Read it back
• Ask the user some questions
• Write the real config file

This means if you press ctrl+c during those questions, you'll be left in a broken state, and you'll need to delete and re-create the .fauna-project file.