[WIP] One Sattelite Pollster to rule them all

reuse pipeline concept (transformers, resources, publishers)
but change the logic "one pollster == one meter"␣
by "one pollster == many metrics"

A sattelite pollster give to user the possibilty to fetch
and filter metrics from resources and publish them using publishers
through pipeline(s).

Basic rules applied by the pollster:
Create a timer (thread) for each different intervals.
if 2 pipelines have different intervals OR differents resources,
pollster will be run twice in separate thread (syncrhonized)
with his correspondant publisher context
if 2 pipelines have same intervals AND same resources, pollster
will be run once with all pipelines chained.

Todo :
* unittest
* doc
* filtering metrics by regexp
* transformer : mean of of all r'gpu[0-9]_cpu'

imlements bp applications-metrics-from-instances

Change-Id: I0fdd6691a22d715d573c1086d1a5df1827855167