Pass the backup username and password to mysql when running SHOW DATABASES in
mysqlbackup.sh if `file_per_database` is true and `backupdatabases` is empty.
This script could be used to sync backups to a central server, or just
to create a file to let external scripts know that backups are
(sucessfully) done and can be picked up.
The postscript option (defaults to false) and can be either a string or
an array of strings. These strings will be directly put into the
mysqlbackup.sh and as such can either be shell commands, or externally
managed files.
These tests are more or less parity with the rspec-system tests, though
dependent on a few patches that still have to make it into beaker and
beaker-rspec
