Fix quoting of $@ and don't exec in the background.
Fix quoting of $@ and don't exec in the background.

"$@" expands to "$1" "$2" "$3" which preserves spaces calling the chained command.

"$*" expands to "$1 $2 $3" which makes sense for the echo argument.

This commit also switches to simply calling the chained command in the
foreground, instead of exec in the background with wait which is
a complicated way of doing nothing.

BetterWorks/heroku-buildpack-pgbouncer,rmoorman/heroku-buildpack-pgbouncer,realtymaps/heroku-buildpack-pgbouncer,Yobota/heroku-buildpack-pgbouncer,agriffis/heroku-buildpack-pgbouncer,Shyp/heroku-buildpack-pgbouncer,heroku/heroku-buildpack-pgbouncer