Added possibility to sort jobs by Duration column which is a property but not a field in the model.
Added possibility to sort jobs by Duration column which is a property
but not a field in the model.

Change-Id: I75e949a0e515b23db013606b484fd300405e209e
Reviewed-on: http://staging.review.linaro.org/552
Reviewed-by: lava-bot <f1c518755f92a4c3b69132fe31fc3cc1dae5545f@linaro.org>
Reviewed-by: Neil Williams <7fa63296f36ddf15e756692583a73cae1716234f@linaro.org>

Linaro/lava-server,OSSystems/lava-server,OSSystems/lava-server,Linaro/lava-server,OSSystems/lava-server,Linaro/lava-server,Linaro/lava-server