Thread: pgsql: When a TAP file has non-zero exit status, retain temporary direc

When a TAP file has non-zero exit status, retain temporary directories.

PostgresNode already retained base directories in such cases.  Stop
using $SIG{__DIE__}, which is redundant with the exit status check, in
lieu of proliferating it to TestLib.  Back-patch to 9.6, where commit
88802e068017bee8cea7a5502a712794e761c7b5 introduced retention on
failure.

Reviewed by Daniel Gustafsson.

Discussion: https://postgr.es/m/20200202170155.GA3264196@rfd.leadboat.com

Branch
------
REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/78a26c3edd85b439265c067c45f04ce017c2eaff

Modified Files
--------------
src/test/perl/PostgresNode.pm | 17 +----------------
src/test/perl/TestLib.pm      |  9 +++++++--
2 files changed, 8 insertions(+), 18 deletions(-)