Check duplicates on "Table Name => internal index id mappings" data dictionary

[yoshinorim]

create table t (id int primary key ) engine=rocksdb;
insert into t values (1), (2), (3);
$ rm /data/test/t.frm
flush tables;
create table t (id int primary key, value int ) engine=rocksdb;
=> Succeeded
select * from t;
=> Empty Set

MyRocks needs to be more robust so that second create table fails.