Adjust pgbench option for debug mode.

Adjust pgbench option for debug mode.

Many other utilities use -d to specify the database to use, but
pgbench uses it to enable debug mode.  This is causing some users
to accidentally enable it.  This commit changes -d to accept the
database name and introduces --dbname.  Debug mode can still be
enabled with --debug.  This is a backward-incompatible change, but
it has been judged to be worth the trade-off, i.e., some scripts
that use pgbench will need to be updated.

Author: Greg Sabino Mullane
Reviewed-by: Tomas Vondra, Euler Taveira, Alvaro Herrera, David Christensen
Discussion: https://postgr.es/m/CAKAnmmLjAzwVtb%3DVEaeuCtnmOLpzkJ1uJ_XiQ362YdD9B72HSg%40mail.gmail.com