[nova] [placement] Proposing Sean Mooney as nova-core

Hi all, I would like to propose Sean as an addition to the nova-core team (which includes placement merge rights as nova-core is implicitly a subgroup).

As we know, he's around for a long time, is already a nova-specs-core and has proven solid experience in reviews.

Cores, please vote (-1, 0, +1) before next Wednesday Jan 19th 1600UTC.

Cheers, -Sylvain