Added hardware agent's inspector and snmp implementation

Added the inspector interface to hardware agent, also added the snmp
implementation of that inspector.

Implements: blueprint monitoring-physical-devices

Based on the original code at https://github.com/graflu0/ceilometer
contributed by Lucas and Toni.

Change-Id: I7cbaf94d72d389dc802c42b6ca8939b81a1d6b10
Signed-off-by: Lucas Graf <graflu0@students.zhaw.ch>
Signed-off-by: Toni Zehnder <zehndton@students.zhaw.ch>
Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>
Added hardware pollsters for the central agent

This patch added various pollsters for the hardware agent.

Implements: blueprint monitoring-physical-devices

Based on the original code at https://github.com/graflu0/ceilometer
contributed by Lucas and Toni.

Signed-off-by: Lucas Graf <graflu0@students.zhaw.ch>
Signed-off-by: Toni Zehnder <zehndton@students.zhaw.ch>
Signed-off-by: Lianhao Lu <lianhao.lu@intel.com>

Change-Id: Id259b95efdbf0b7d03b657586d588f9637d9a367
Merge "Added hardware agent's inspector and snmp implementation"
Merge "Added hardware pollsters for the central agent"