Add option to exclude certain databases

[robrwo]

For our purposes, we don't need to backup the mysql, performance_schema or information_schema databases, so would like to exclude them from backups.

We can modify the mysqlbackup.sh.erb template with something like:

mysql -s -r -N -e 'SHOW DATABASES' <% if ! @excludedatabases.empty? %> | grep -v '^\(<% @excludedatabases.join('|') %>)$' <% end %> | while read dbname

[Aaron-Rob]

Hello! We are doing some house keeping and noticed that this issue has been open for a long time. We're going to close it but please do raise another issue if the issue still persists. 😄