Ported commit fab791bc805f95d59c55cbcb554e6f218710b0dd from castor/master
CASTOR-4836: tapeserverd should have a new time counter: delivery time Fixed. Add two counters: deliveryTime and drainingTime. For the recall session deliveryTime is the total time of the disk threads and drainigTime is the time difference between deliveryTime and the total time of the tape thread or in other words how much time disk threads spent after the tape thread finished. For the migration session deliveryTime is the total time of the tape thread and drainingTime always equal 0.