sstableloader outputs progress information and summary stats to stderr instead of stdout

On Cassandra 2.1.0+, the progress information from sstableloader is output into the stderr stream instead of stdout.

This can be reproduced by running an sstableloader and redirecting stderr to a file:

sstableloader -d 127.0.0.1 /home/automaton/cassandra-src/data/data/keyspace1/standard1-abfab2e0ccb811e49d4417363885fa00 2> error.log