pgsql: Set random seed for pgbench.

Set random seed for pgbench.

Setting random could increase reproducibility of test in some cases. Patch
suggests three providers for seed: time (default), strong random
generator (if available) and unsigned constant. Seed could be set from
command line or enviroment variable.

Author: Fabien Coelho
Reviewed by: Chapman Flack
Discussion: https://www.postgresql.org/message-id/flat/20160407082711(dot)q7iq3ykffqxcszkv(at)alap3(dot)anarazel(dot)de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/64f85894ad2730fb1449a8e81dd8026604e9a546

Modified Files
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doc/src/sgml/ref/pgbench.sgml | 42 +++++++++++++++++
src/bin/pgbench/pgbench.c | 69 +++++++++++++++++++++++++---
src/bin/pgbench/t/001_pgbench_with_server.pl | 69 +++++++++++++++++++++++++---
src/bin/pgbench/t/002_pgbench_no_server.pl | 2 +
4 files changed, 170 insertions(+), 12 deletions(-)