Move metering_secret to publisher section

In Icehouse, metering_secret has been moved to [publisher]:
http://git.io/11NwNw

Change-Id: I96c70781902e927c0295af78c93b400d7b4684bb
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Don't match commented [DEFAULT]

Class ceilometer::agent::compute fails when there are [DEFAULT] sections
commented. This patch is fixing this issue. For more info check
https://bugzilla.redhat.com/show_bug.cgi?id=1060712

Change-Id: I6d13f780f63af8798d94b49246576d1e144a4540
Merge "Move metering_secret to publisher section"