storage_proxy: handle intentional short reads
storage_proxy: handle intentional short reads

If the result is going to be too large the replica may decide to make it
shorter and coordinator should handle this properly (i.e. do not retry).
Moreover, coordinator could avoid some retries by setting the short_read
flag itself.

Signed-off-by: Paweł Dziepak <e29bb3265626c60caf76d587cabdfcd8b379ef80@scylladb.com>

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