pgsql: In pg_regress, remove the temporary installation upon successful

In pg_regress, remove the temporary installation upon successful exit.

This results in a very substantial reduction in disk space usage during
"make check-world", since that sequence involves creation of numerous
temporary installations. It should also help a bit in the buildfarm, even
though the buildfarm script doesn't create as many temp installations,
because the current script misses deleting some of them; and anyway it
seems better to do this once in one place rather than expecting that
script to get it right every time.

In 9.4 and HEAD, also undo the unwise choice in commit b1aebbb6a86e96d7
to report strerror(errno) after a rmtree() failure. rmtree has already
reported that, possibly for multiple failures with distinct errnos; and
what's more, by the time it returns there is no good reason to assume
that errno still reflects the last reportable error. So reporting errno
here is at best redundant and at worst badly misleading.

Back-patch to all supported branches, so that future revisions of the
buildfarm script can rely on this behavior.

Branch
------
REL9_2_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/89b6a19e1cc9536e782a132b551a5e642db9972a

Modified Files
--------------
src/test/regress/pg_regress.c | 13 +++++++++++++
1 file changed, 13 insertions(+)