The `sbd` stage operation on a down cluster should be rejected immediately

[zzhou1]

As the title, using the sbd stage to migrate the "disk-based sbd" cluster to "diskless sbd" leads to an incomplete sbd configuration without an error reported, eg. missing stonith-watchdog-timeout.

Here is the reproducer:

adm@160-1:~> sudo -E crm cluster init -ys /dev/disk/by-partlabel/sbd-160 -N adm@160-2
adm@160-1:~> sudo -E crm cluster stop --all

adm@160-1:~> sudo -E crm cluster init sbd -yS
INFO: Loading "default" profile from /etc/crm/profiles.yml                                                                                                                                                          
INFO: Loading "knet-default" profile from /etc/crm/profiles.yml                                                                                                                                                     
WARNING: Pacemaker state transition is in progress. Skip restarting cluster in maintenance mode.                                                                                                                    
INFO: Configuring diskless SBD                                                                                                                                                                                      
WARNING: Diskless SBD requires cluster with three or more nodes. If you want to use diskless SBD for 2-node cluster, should be combined with QDevice.                                                               
INFO: Update SBD_WATCHDOG_TIMEOUT in /etc/sysconfig/sbd: 15                                                                                                                                                         
INFO: Update SBD_WATCHDOG_DEV in /etc/sysconfig/sbd: /dev/watchdog0                                                                                                                                                 
INFO: Done (log saved to /var/log/crmsh/crmsh.log on 160-1)