pgsql: Make pg_rewind test case more stable.

Make pg_rewind test case more stable.

If replication is exceptionally slow for some reason, pg_rewind might run
before the test row has been replicated. Add an explicit wait for it.

Reported-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/20201120003811.iknhqwatitw2vvxf%40alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c71f9a094b32770dcd34b9ba4909435e34583747

Modified Files
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src/bin/pg_rewind/t/007_standby_source.pl | 4 ++++
1 file changed, 4 insertions(+)