pgsql: In the pg_rewind test suite, receive WAL fully before promoting.

In the pg_rewind test suite, receive WAL fully before promoting.

If a transaction never reaches the standby, later tests find unexpected
cluster state.  A "tail-copy: query result matches" test failure has
been the usual symptom.  Among the buildfarm members having run this
test suite, most have exhibited that symptom at least once.  Back-patch
to 9.5, where pg_rewind was introduced.

Michael Paquier, reported by Christoph Berg.

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/58feb1a94a5ea0ae3395b1818ba76ab68485a7a4

Modified Files
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src/bin/pg_rewind/RewindTest.pm |   14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)