We consider BEEFY mature enough to run by default on all nodes
for test networks (Rococo/Wococo/Versi).

Right now, most nodes are not running it since it's opt-in using
--beefy flag. Switch to an opt-out model for test networks.

Replace --beefy flag from CLI with --no-beefy and have BEEFY
client start by default on test networks.

Signed-off-by: acatangiu <adrian@parity.io>