crush: support new indep mode and SET_* steps (crush v2) by default

Add CRUSH_V2 feature (new indep mode and SET_* steps) to a set of
features supported by default.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>