[LUCID] We need "limit" Upstart-ed ssh respawning

ssh is now handling by upstart native jobs(with /etc/init/ssh.conf configs), and "respawn" stanza. This is great works. But this behavior is not familiar for security paranoid.

Scenario:
  - sshd is enougth to berief, but this is not perfect. In future, if we have got vuln for exploiting sshd, that can "randomly" type atacks (e.g.: buffer overflow, it is exploitable with probabilistic atacks, like brute force.).
  - endless respawning is weaken for these "memory address brute force" atacks.

IMHO, when using "respawn" stanza, it needs something "limit" stanza (e.g.: respawn limit 60 30)
or any other way ( e.g.: MAC by AppArmor).

limitation by "limit" can mitigates(atack speed limitation) probabilistic atacks.
This limitation provides potential over-limit DoS, but unlimited respawning is dangerous.

# May be, we have to improvement upstart respawn stanza, like "respawn delay"
# feature...(see https://bugs.launchpad.net/upstart/+bug/252997)

....Yes, this wish is not only ssh services. But ssh is most popular + internet accessible services.
In general cases, administrator use "ufw limit ssh" settings. Its not hazardous.