Remove logback.xml from .gitignore

And add the midonet-brain/conf/logback.xml file for the cluster.

Change-Id: I768792f51bd68809514c7aeb3a8e83b311755f7a
Signed-off-by: Galo Navarro <galo@midokura.com>
Merge "Remove logback.xml from .gitignore"