Fix variety name for trickle_credit

This commit fixes the discrepancy between the trickle up message tag
used by the vboxwrapper and the tag expected by sched/trickle_credit.pp.

Signed-off-by: Carlos Aguado Sanchez <carlos.aguado@epfl.ch>
Add logging for the trickle operation

Signed-off-by: Carlos Aguado Sanchez <carlos.aguado@epfl.ch>