CREATE TABLE IF NOT EXISTS PARTITION OF raise error instead of just skip

[gwierzchowski]

CREATE TABLE "test2" (
   "cdc" INTEGER,
   "product" INTEGER)
PARTITION BY LIST ("cdc");
-- ok
SELECT create_distributed_table('test2', 'product');
-- ok
CREATE TABLE "test2_1" PARTITION OF "test2" for values in (1);
-- ok
CREATE TABLE IF NOT EXISTS "test2_1" PARTITION OF "test2" FOR VALUES IN (1); 
NOTICE:  relation "test2_1" already exists, skipping
ERROR:  table "test2_1" is already distributed

It should just give notice without error (how it is on plain PG).
Under Python this raises psycopg2.ProgrammingError.

Citus 7.3, PG 10.3 started from docker-compose on Linux Mint 18.3

[ozgune]

@gwierzchowski -- Thank you for reporting this bug.

@metdos -- Do we know how long the fix would take?

[l-we]

Is there any progress