BUG #14875: pg_createcluster fails to load --createclusterconf

The following bug has been logged on the website:

Bug reference: 14875
Logged by: Bradley Ouellette
Email address: bouellette(at)mixpo(dot)com
PostgreSQL version: 9.4.14
Operating system: Ubuntu 14.04.5 LTS
Description:

Unfortunately pg_createcluster doesn't have a version option to reference.

This works in the version installed in 174.pgdg14.04+1 but fails in version
186.pgdg14.04+1

Running:
pg_createcluster --createclusterconf=setup/restore-cluster.conf 9.4
restore4
Creates a new instance that has a default
/etc/postgresql/9.4/restore4/postgresql.conf which lacks the options
specified in the restore-cluster.conf config file. It also lacks any
customizations in /etc/postgresql-common/createcluster.conf (tested by just
replacing the default /etc/postgresql-common/createcluster.conf file with
the custom version we are using.

Running
pg_createcluster 9.4 restore4 correctly updates the default values as
specified in /etc/postgresql-common/createcluster.conf

We like using the alternate config location since it allows us to keep that
file inside out source code repo.

The pg_createcluster works correctly if I copy the older version of that
utility from

Further Investigation:
The new Version on Line 29 has: chdir '/';
The createclusterconf option works if I specify a full path to the file. If
the utility needs a full path, The documentation should note that.

Also if it doesn't find the alternate file I would expect it to fall back on
the default(or fail gracefully), and print a warning that the file isn't
found.