Support placement for autoid

[lcwangchao]

autoid meta is stored in tikv to generate table id/auto increment keys. However, currently we can not set placement rules for it and this may cause some problems. For example, user may use to placement rule to place all data in places where have a lower network latency. But autoid meta still has a probability of being scheduled to some "slower" places that will cause the "insert" operation slowly (not every time, because it has a cache).

I think it is reasonable for autoid meta to follower the table's placement rules.