Add gen block check time

[gasby88]

Add gen block check time to reduce the time of trigger off change view.

Signed-off-by: wangbing [email protected]

[Arbio5zt]

approve

[gasby88]

Yes，the main change is reduce the time of backup nodes request change view when the net cannot make consensus. When the primary node dead or other circumstance, the backup nodes mast wait 2 gen block time to trigger off change view, but now only need to wait a gen block time and a gen block check time。