pgsql: Don't hardcode contrib_regression dbname in postgres_fdw and dbl

Don't hardcode contrib_regression dbname in postgres_fdw and dblink tests.

That allows parallel installcheck to succeed inside contrib/. The
output is not particularly pretty unless make's -O option to
synchronize the output is used.

There's other tests, outside contrib, that use a hardcoded,
non-unique, database name. Those prohibit paralell installcheck to be
used across more directories; but that's something for a separate
patch.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ddc2504dbcf2af97b58a91b071768c17774d58d1

Modified Files
--------------
contrib/dblink/Makefile | 3 --
contrib/dblink/expected/dblink.out | 43 ++++++++++++----------
contrib/dblink/sql/dblink.sql | 45 ++++++++++++++----------
contrib/postgres_fdw/Makefile | 3 --
contrib/postgres_fdw/expected/postgres_fdw.out | 8 +++--
contrib/postgres_fdw/sql/postgres_fdw.sql | 8 +++--
6 files changed, 64 insertions(+), 46 deletions(-)