Use oslo's log

This patch imports oslo's log module. I modified it since it depends on
oslo's notifier which has many other dependencies Marconi doesn't need.

There's sort of an issue with gunicorn, it seems that once
log.setup('marconi') is called, gunicorn starts logging twice each
message.

Change-Id: I85e8354b7af9b67ea1f87e54b3b73250d4a1115a