pgsql: Avoid and detect SIGPIPE race in TAP tests.

Avoid and detect SIGPIPE race in TAP tests.

Don't write to stdin of a psql process that could have already exited
with an authentication failure.  Buildfarm members crake and mandrill
have failed once by doing so.  Ignore SIGPIPE in all TAP tests.
Back-patch to v10, where these tests were introduced.

Reviewed by Michael Paquier.

Discussion: https://postgr.es/m/20171209210203.GC3362632@rfd.leadboat.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/ac93acbc05be2ef995208c1ca17f8083f60ccc53

Modified Files
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src/test/authentication/t/001_password.pl | 3 +--
src/test/authentication/t/002_saslprep.pl | 3 +--
src/test/perl/TestLib.pm                  | 4 ++++
3 files changed, 6 insertions(+), 4 deletions(-)