pgsql: initdb: Use atexit()

initdb: Use atexit()

Replace exit_nicely() calls with standard exit() and register the
cleanup actions using atexit().  The coding pattern used here mirrors
existing use in pg_basebackup.c.

Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/ec4135ba-84e9-28bf-b584-0e78d47448d5@2ndquadrant.com/

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/3913a40ff104fd26f795c3d4c402ec27a1f86385

Modified Files
--------------
src/bin/initdb/initdb.c | 82 ++++++++++++++++++++++++++-----------------------
1 file changed, 43 insertions(+), 39 deletions(-)