`crm sbd configure` should improve error handling when ssh is unreachable

[zzhou1]

As the title, here is the current situation. In the error condition when ssh is unreachable, sbd metadata is changed but not for sysconfig. It's a bit "surprising" impression about the discrepancy at the first place.

1. The error message only mention "systemctl is-enabled sbd.service", that is nothing user oriented information. Maybe add a WARNING after the ERROR, to provide information users do care, something like,

   WARNING: sbd sysconfig has no change, and can mismatch to the sbd disk metadata due to the above ERROR.

adm@tw-1:~> sudo crm sbd conf watchdog-timeout=120
...
ERROR: sbd.configure: Failed to run command systemctl is-enabled 'sbd.service' on adm@tw-1: adm@tw-1: Permission denied (publickey,password,keyboard-interactive). Environment variable SSH_AUTH_SOCK does no
t exist. Please check whether ssh-agent is available and consider using "sudo --preserve-env=SSH_AUTH_SOCK".                                                                                                       

adm@tw-1:~> sudo -E crm sbd configure show sysconfig grep DELAY
Timeout (msgwait)  : 120
SBD_DELAY_START=71

adm@tw-1:~> sudo -E crm sbd conf watchdog-timeout=120
adm@tw-1:~> sudo -E crm sbd configure show|grep -e DELAY -e msgwait
Timeout (msgwait)  : 240
SBD_DELAY_START=281

2. Furthermore, if any node is unreachable, it is not safe (or, perhaps better not allow) to change any sbd static configuration. That says, only crm sbd configure show and crm sbd status are doable in such case.

[liangxin1300]

For those No ssh customers, maybe we should let the user walk through the whole process, in local mode

[liangxin1300]

How about we add --local option for sbd configure, sbd device and sbd purge, for those ssh unavailable cases

[liangxin1300]

# crm sbd configure watchdog-timeout=120
WARNING: host "alp-2" is unreachable
ERROR: sbd.configure: There are nodes unreachable: alp-2
Please check the network connectivity before configuring SBD.

In #1860