This option provides REINDEX (TABLESPACE) for reindexdb, applying the
tablespace value given by the caller to all the REINDEX queries
generated.

While on it, this commit adds some tests for REINDEX TABLESPACE, with
and without CONCURRENTLY, when run on toast indexes and tables.  Such
operations are not allowed, and toast relation names are not stable
enough to be part of the main regression test suite (even if using a PL
function with a TRY/CATCH logic, as CONCURRENTLY could not be tested).

Author: Michael Paquier
Reviewed-by: Mark Dilger, Daniel Gustafsson
Discussion: https://postgr.es/m/YDiaDMnzLICqeukl@paquier.xyz