``DB_PASSFILE`` is split into ``HOST_DB_PASSFILE`` and ``CLIENT_DB_PASSFILE`` to allow
to use a ``HOST_DB_PASSFILE`` in a directory that is accessible to ``compose`` even when
run in docker mode.
Using this, we can store HOST_DB_PASSFILE along with the database files,
which makes a lot more sense as it resolv issues of synchronising the
database with the content of this file (namely, the authorization
scheme). So when restoring the datastore of the database, the charm
scripts will be able to use the db password file and will not have to
worry about if it is in sync with the files or not.
Note that ``db_docker_opts`` and ``db_cmd_opts`` are now bash arrays. As
previous implementation was brittle, especially for handling spaces in
arguments.