Added resources definition in the pipeline

The 'resources' in the pipeline definition is a list of endpoints for
the pollsters to get the data from. It's optional and it's up to the
specific pollsters to decide how to use it.

The new pipeline definition could be something like the following:

    meters:
        - "*"
    resources:
        - file:///foo/bar/endpoints

Implements: blueprint support-resources-pipeline-item
Change-Id: Ibd7426f8f453c176c99d3786106deb35bbac8d4f
Merge "Added resources definition in the pipeline"