[PATCH] Move user options to the end of the command in pg_upgrade

Hi,

when the environment variable POSTGRESQL_UPGRADE_PGUPGRADE_OPTIONS is
used to specify options for pg_upgrade, options related to
unix_socket_directory/ies are being overridden by hardcoded options,
making it difficult to upgrade in some usecases.

The attached patch changes the order of those options so that the
hardcoded ones are eventually overridden by the user specified
options.

As I can see that in PostgreSQL 12 this issue has been solved by
implementing the -socketdir argument, my questions would be as
follows:

1) Could such change break something that I might have missed?
2) Would you be willing to accept this patch for versions prior to 12?

Thanks in advance.

--
Patrik Novotný

Associate Software Engineer

Red Hat

panovotn(at)redhat(dot)com