Added a new scheduler metrics weight plugin

[OpenStack Infra]

https://review.openstack.org/35765
commit bc32777e73904506d5900487fe98944a26ee5b23
Author: Lianhao Lu <email address hidden>
Date: Thu Jun 27 17:54:30 2013 +0800

    Added a new scheduler metrics weight plugin

    The new metrics weigher can compute the weight based on the compute
    node host's metrics data. The to-be weighed metrics and their
    weighing ratio are specified in the configuration file as the
    followings:

        metrics_weight_setting = name1=1.0,name2=-1.0

    The final weight would be name1.value * 1.0 + name2.value * (-1.0).

    This is part of the blueprint utilization-aware-scheduling.

    DocImpact

    Change-Id: Ib3e68505e6d4d8f6d67b54c5f00de3e1c172738c

[Summer Long (slong-g)]

This was added into the Config Ref 'Weights' section in: https://review.openstack.org/#/c/87446
Closing currentRelease.