scylla-gdb.py: redo find_db() in terms of sharded()
scylla-gdb.py: redo find_db() in terms of sharded()

Signed-off-by: Michael Livshin <ae60993c65de9cdf2ca07b7426c976808535d555@scylladb.com>

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