pgsql: Set application_name per-test in isolation and ecpg tests.

Set application_name per-test in isolation and ecpg tests.

Commit a4327296d taught pg_regress proper to do this, but
missed the opportunity to do likewise in the isolationtester
and ecpg variants of pg_regress. Seems like this might be
helpful for tracking down issues exposed by those tests.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/b1907d6882205319822c7452ce6b5e71ee2867be

Modified Files
--------------
src/interfaces/ecpg/test/pg_regress_ecpg.c | 8 ++++++++
src/test/isolation/isolation_main.c | 7 +++++++
src/test/regress/pg_regress.c | 4 ++++
3 files changed, 19 insertions(+)