JobShell delete all locks

It is convenient if JobShell can delete all locks with a single command. This is useful, for example, when a container using cron is running jobShell processes and exits (via SIGTERM) to make sure that all locks are removed.

The design proposal here is to allow the syntax

./Console/cake Job -U all

to then invoke

return $this->deleteAll('TRUE');

on the Lock model.

Here 'TRUE' is an SQL fragment that is understood with the WHERE clause by both MySQl and PostgreSQL.