upstart: start ceph-all on runlevel [2345]

Starting when only one network interface has started breaks machines with
multiple nics in very problematic ways.

There may be an earlier trigger that we can use for cases where other
services on the local machine depend on ceph, but for now this is better
than the existing behavior.

See #5248

Signed-off-by: Sage Weil <sage@inktank.com>