pgsql: Indicate session name in isolationtester notices

Indicate session name in isolationtester notices

When a session under isolationtester produces printable notices (NOTICE,
WARNING) we were just printing them unadorned, which can be confusing
when debugging.  Prefix them with the session name, which makes things
clearer.

Author: Álvaro Herrera
Reviewed-by: Hari Babu Kommi
Discussion: https://postgr.es/m/20181024213451.75nh3f3dctmcdbfq@alvherre.pgsql

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a28e10e82e540d45e448bc404af76df8a54008f1

Modified Files
--------------
.../isolation/expected/vacuum-concurrent-drop.out  |  6 ++---
src/test/isolation/expected/vacuum-conflict.out    | 16 +++++------
src/test/isolation/expected/vacuum-skip-locked.out | 16 +++++------
src/test/isolation/isolationtester.c               | 31 ++++++++++++++++++++++
4 files changed, 50 insertions(+), 19 deletions(-)