Enable marconi-server to run when USE_SCREEN=false

This patch,
1. adds log_file option to marconi.conf
2. redirects the output from marconi-server, in the same precedent
set by another project.

Change-Id: Ib273a03625d5a4edf8bb3ed7d522d2b087975acd
Merge "Enable marconi-server to run when USE_SCREEN=false"