pgsql: Improve speed of contrib/postgres_fdw regression tests.

Improve speed of contrib/postgres_fdw regression tests.

Commit 7012b132d added some tests that consumed an excessive amount of
time, more than tripling the time needed for "make installcheck" for this
module. Add filter conditions to reduce the number of rows scanned,
bringing the runtime down to within hailing distance of what it was before.

Jeevan Chalke and Ashutosh Bapat, per a gripe from me

Discussion: https://postgr.es/m/16565.1478104765@sss.pgh.pa.us

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/aa7f593b1ffa9717bd5570174944c06c482d1c1f

Modified Files
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contrib/postgres_fdw/expected/postgres_fdw.out | 36 +++++++++++---------------
contrib/postgres_fdw/sql/postgres_fdw.sql | 12 ++++-----
2 files changed, 21 insertions(+), 27 deletions(-)