Ensure that child table inherits distribution stretegy from the parent.

Ensure that child table inherits distribution stretegy from the parent.

For partitioned tables or in general inherited tables, we now enforce that the
child table always inherit the distribution strategy of the parent. This not
only makes it far easier to handle various cases correctly, but would also
allow us to optimise distributed queries on partitioned tables much easily.

Tank.zhang <6220104@qq.com> originally reported a problem with partitioned
tables and incorrect query execution. Upon investigations, we decided to make
these restrictions to simplify things.