pgsql: Avoid unfortunate IPC::Run path caching in PostgresNode

Avoid unfortunate IPC::Run path caching in PostgresNode

Commit b34ca595ab provided for installation-aware instances of
PostgresNode. However, it turns out that IPC::Run works against this by
caching the path to a binary and not consulting the path again, even if
it has changed. We work around this by calling Postgres binaries with
the installed path rather than just a bare name to be looked up in the
environment path, if there is an installed path. For the common case
where there is no installed path we continue to use the bare command
name.

Diagnosis and solution from Mark Dilger

Discussion: https://postgr.es/m/E8F512F8-B4D6-4514-BA8D-2E671439DA92@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/95c3a1956ec9eac686c1b69b033dd79211b72343

Modified Files
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src/test/perl/PostgresNode.pm | 36 +++++++++++++++++++++++++++++++-----
1 file changed, 31 insertions(+), 5 deletions(-)