Metering LoadBalancer as a Service

This adds support for measurements around LBaaS.
Added Pollsters to track Load balancer Pools, Vips,
members and Health Probes. Also includes statistics
pollsters to track total_connections, active_connections
and bandwidth.

Included test coverage for Neutron client and LBaaS
pollsters.

Change-Id: Ia0570a824e099c341c8f12f95f576dfb8b1fdfc4
Partially Implements: blueprint ceilometer-meter-lbaas
Merge "Metering LoadBalancer as a Service"