Adds metrics collection support in Hyper-V

Adds metrics collection support in Hyper-V

Blueprint: hyper-v-metrics

Hyper-V Server 2012 supports a new set of metrics API that can be used to
provide switch port metrics data to external applications, e.g. Ceilometer.

Metrics collection is disabled by default and can be enabled with a config
option.

Metrics are configured via ACLs applied by the Hyper-V plugin agent.

Change-Id: Ife2a53db84936bae7c73b8c027022bbc5e89d48a