pgsql: Improve wait logic in TAP tests for streaming replication.

Improve wait logic in TAP tests for streaming replication.

Remove hard-wired sleep(2) delays in 001_stream_rep.pl in favor of using
poll_query_until to check for the desired state to appear. In addition,
add such a wait before the last test in the script, as it's possible
to demonstrate failures there after upcoming improvements in pg_ctl.

(We might end up adding polling before each of the get_slot_xmins calls in
this script, but I feel no great need to do that until shown necessary.)

In passing, clarify the description strings for some of the test cases.

Michael Paquier and Craig Ringer, pursuant to a complaint from me

Discussion: https://postgr.es/m/8962.1498425057@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/5c77690f6f419c504b7d8248db30c2280217e72e

Modified Files
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src/test/recovery/t/001_stream_rep.pl | 65 ++++++++++++++++++++++++-----------
1 file changed, 45 insertions(+), 20 deletions(-)