Unify the sensor data format

Ceilometer will consider the 'Sensor Reading' data contains the unit in
the end of current value, ipmitool driver returns such format, however our
ipminative driver returns the 'Sensor Reading' value without the unit, so we
have to unify them for Ceilometer to provide same sensor data format.

Closes-Bug: #1367620

Change-Id: I6796bf513730259b7a27715252a72879b11d3bae
Merge "Unify the sensor data format"