Cleanup device backend cache on exit.
Fix problem with getting symlink data on windows.
Debian: fixes migrating from psql with password

Prevents a problem if migrating from a version without dbconfig to a version with dbconfig
and have a postgresql database with password access.
Debian: fixes a problem when migrating to dbconfig

The Bareos database maintenance scripts for the postgres backend
create the Bareos database using the database administrator account
and grant permission to the Bareos database user.
When a Bareos update requires a database schema update,
the user has to call
update_bareos_tables
and
grant_bareos_privileges.

When using dbconfig (Bareos >= 14.1),
only update_bareos_tables is performed,
as grant_bareos_privileges would require variable substitutions (db_name, db_user and db_password),
which is not supported in dbconfig (dbc_sql_substitutions only works on installing, not on updates).
Therefore it is necessary, that new tables are created as the Bareos database user,
so it automatically has sufficient permissions.
As the Bareos database user can not drop tables not created by himself,
the drop statement must be executed as database administrator user.

This patch implements this.

The resuls to:

Updating from Bareos < 14.1:
database: owner postgres
tables already existing before 14.1: owner postgres, permission to baroes
tables created after 14.1: owner bareos

Installing Bareos >= 14.1:
database: owner bareos
tables:   owner bareos

Fixes #380: Debian: when migrating from 13.2 to 14.2 with postgres backend, database permissions are not set correctly
Work around the fact that the usermod doesn't always have -a

Fixes #382: Don't remove supplemental groups on install.