Multiple publisher pipeline framework

With multiple publisher support, a meter data can be sent to multiple
conduit, like message bus, CW API etc.

Pipeline framework transfers the data from pollster and notification
handler to the publisher, through multiple pipelines.
Each pipeline is composed of 1 or more transformers and one or more
publishers. The transformer transforms the data, like summary, drop,
delta etc.

For bp: multi-publisher

Change-Id: Iff8b85d724eb6358d147b8a8431837934d913c88
Signed-off-by: Yunhong, Jiang <yunhong.jiang@intel.com>