Ceilometer Config element for custom pipeline

-These elements are for overwriting of default pipeline.yaml
 defined in ceilometer element install.d

There should a be config element taking json configuration,
though that is non-trivial problem that will likely go
in a follow up patch.

Change-Id: Ib0035f5a4359885a9a30c98fdecb86b940e9cb6a
Merge "Ceilometer Config element for custom pipeline"