Обсуждение: pgsql: Make src/test/recovery/t/017_shm.pl safe for concurrentexecutio

Make src/test/recovery/t/017_shm.pl safe for concurrent execution.

Buildfarm members idiacanthus and komodoensis, which share a host, both
executed this test in the same second.  That failed.  Back-patch to 9.6,
where the test first appeared.

Discussion: https://postgr.es/m/20190404020543.GA1319573@rfd.leadboat.com

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0e0d449fb02ae42b97f9a3b4ccf956fbb1e64565

Modified Files
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src/test/recovery/t/017_shm.pl | 33 ++++++++++++++++++++++++++++-----
1 file changed, 28 insertions(+), 5 deletions(-)