Turn reseed_dead_plants on by default for AD spinup mode

[ekluzek]

We talked about this in a CTSM software meeting and also in a meeting talking about the matrix spinup process. By default reseed_dead_plants should be turned on at the start of AD spinup mode. That's the time that it should always be on. There are also times when it should be turned on for other circumstances, but the user will have to figure those cases out. In general the idea is that if plants can't survive in AD spinup mode, they should really stay dead. So you wouldn't turn it on for other spinup modes.