journald: add configuration option for enabling/disabling audit during journald startup

journald: add configuration option for enabling/disabling audit during journald startup

Let's make it optional whether auditing is enabled at journald start-up
or not.

Note that this only controls whether audit is enabled/disabled in the
kernel. Either way we'll still collect the audit data if it is
generated, i.e. if some other tool enables it, we'll collect it.

Fixes: #959