Fix Swift config for Ceilometer usage

Ceilometer filter was previously removed from the Swift
configuration to avoid useless Ceilometer logs in the Swift
ones. This was fixed by setting only warning log level for
this Ceilometer part of the pipeline to keep only important
ones.

Change-Id: I8c41355bb98dbf3bb59ec792221b05ea936086b7
Partial-Bug: #1294789
Merge "Fix Swift config for Ceilometer usage"
Merge commit 'refs/changes/83/86083/2' of git://gold.eng.hq.xensource.com/git/github/openstack-dev/devstack into tmpbranch