my_temptablespace2: don't check cache for pg_default/pg_global

Without checking this, a segfault is caused on bootstrap process. And as
those are never temporary, we don't need to check the cache for those
(it is a cut-off).
my_temptablespace2: create subdirectory structure on-demand (only for temp tablespaces)
my_temptablespace2: check if spcoptions is set (e.g. not null)
my_temptablespace2: add regression tests