when starting multiple tasks using `consul lock` should be an option

To prevent a thundering herd it would be great if nomad supported `consul lock` in some fashion so that I could upgrade a hundred jobs in a controlled fashion. A key feature would be to specify the key so that you could lock _across_ different jobs (as well as within a job/group if desired).

I'm aware of `splay` but that's a sub-optimal/nondeterministic solution. Is `1h` long enough? What if my cluster can handle three simultaneous job upgrades and doing all of them would take 20 minutes?

If the `pre_hook`, `post_hook` feature was implemented then maybe a user could hack something together using them. Or this feature could make use of them? My 2 cents on implementation. 😉