pgsql: Ignore partitioned indexes where appropriate

Ignore partitioned indexes where appropriate

get_relation_info() was too optimistic about opening indexes in
partitioned tables, which would raise errors when any queries were
planned on such tables.  Fix by ignoring any indexes of the partitioned
kind.

CLUSTER (and ALTER TABLE CLUSTER ON) had a similar problem.  Fix by
disallowing these commands in partitioned tables.

Fallout from 8b08f7d4820f.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/05fb5d661925f00106373f1a594be5aca24d9a94

Modified Files
--------------
src/backend/commands/cluster.c         | 14 ++++++++++++++
src/backend/optimizer/util/plancat.c   | 10 ++++++++++
src/test/regress/expected/cluster.out  |  8 ++++++++
src/test/regress/expected/indexing.out | 11 +++++++++++
src/test/regress/sql/cluster.sql       |  7 +++++++
src/test/regress/sql/indexing.sql      |  8 ++++++++
6 files changed, 58 insertions(+)