storage_proxy: improve mutation timeout logging
storage_proxy: improve mutation timeout logging

Message-Id: <13db43533b6e995a9e2cfd058ecbfe2d89c05b6f@scylladb.com>

raphaelsc/scylla,scylladb/scylla,raphaelsc/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,kjniemi/scylla,raphaelsc/scylla,kjniemi/scylla,avikivity/scylla