pg_createcluster should not silently ignore locale failure

[Josh Berkus]

Ubuntu Version: 14.04
PostgreSQL version 9.3.5

The way it is now:

1. pg_createcluster will take a --locale switch, in order to initialize the cluster with default emplate databases using, for example, en_US or LATIN1.

2. if pg_createcluster is unable to initdb with that locale (for example, if it's missing in the environment), it **silently fails** and reports success, creating the cluster instead as SQL_ASCII, which format is deprecated by the PostgreSQL project.

3. At that point, the user can happily go on to load all of their data into a database in the wrong encoding, resulting in likely extensive downtimes later to fix the problem, and possible data corruption.

The way it should be:

On step 2, pg_createcluster should fail with an error message.

This is per the documentation, which says that pg_createcluster will do this. However, it is inconsistent and user-hostile behavior, and should be changed.

I do not know at this time whether this undesirable behavior is from the upstream Debian postgresql-common or not.