alternator: fix JSON in DescribeTable response
alternator: fix JSON in DescribeTable response

The structure's name in DescribeTable's output is supposed to be called
"Table", not "TableDescription". Putting in the wrong place caused the
driver's table creation waiters to fail.

Signed-off-by: Nadav Har'El <625169824b719df98706d88646d0aae6f368ae4d@scylladb.com>

scylladb/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla