support meta data cache size limit

[tiancaiamao]

No description provided.

[tiancaiamao]

create table t (id int) with 10000 tables, the memory footprint seems to be 9.34M
It means the normal table size if 956 byte on average.

[tiancaiamao]

create table pt (id int) partition by hash(id) partitions 1024 create 5000 tables, the memory footprint is 2203.9M
It means the partition table size is 451kb on average.