Improve psql's \d output for partitioned indexes.

Include partitioning information much as we do for partitioned tables.
(However, \d+ doesn't show the partition bounds, because those are
not stored for indexes.)

In passing, fix a couple of queries to look less messy in -E output.

Also, add some tests for \d on tables with nondefault tablespaces.
(Somebody previously added a rather silly number of tests for \d
on partitioned indexes, yet completely neglected other cases.)

Justin Pryzby, reviewed by Fabien Coelho

Discussion: https://postgr.es/m/20190422154902.GH14223@telsasoft.com