core: Allow multiple alerts of the same type for host

Add repeatable attribute to AuditLog and AuditLogableBase class which
allows saving multiple alerts of the same type for the same host.

Change-Id: I0deda59438b61c88d45f45af59e85b003f218e1a
Bug-Url: https://bugzilla.redhat.com/1142904
Signed-off-by: Martin Perina <mperina@redhat.com>