Can create a foreign key reference from a local table to a distributed table

We prohibit establishing foreign key relationships between local and distributed tables. It can be circumvented as follows.

### Steps
- Create referenced table (r1)
- Create referer table (r2).
- Connection 1 starts transaction
- - adds foreign key to r2
- Connection 2 starts transaction
- - calls create distributed table on r1
- - gets blocked.
- Connection 1 commits.
- Connection 2 commits.