Fix: utils: Raise UnreachableNodeError for those ssh unreachable nodes (bsc#1250645)

[liangxin1300]

Problem

When SSH is not available at the peer node, configuring sbd will fail and might lead to inconsistent

 # crm sbd configure watchdog-timeout=120
INFO: No 'msgwait-timeout=' specified in the command, use 2*watchdog timeout: 240
INFO: Configuring disk-based SBD
INFO: Initializing SBD device /dev/sda5
INFO: Update SBD_WATCHDOG_DEV in /etc/sysconfig/sbd: /dev/watchdog0
ERROR: sbd.configure: Failed to run command test -d /etc/sysconfig || mkdir -p /etc/sysconfig on root@sle16-2: Cannot create SSH connection to root@sle16-2: ssh: connect to host sle16-2 port 22: Connection refused

See issue #1738

Changed

Raise exception when detecting that any node's SSH port is not reachable

# crm sbd configure watchdog-timeout=120
WARNING: host "sle16-2" is unreachable
ERROR: sbd.configure: There are unreachable nodes: sle16-2.
Please check the network connectivity before configuring SBD.

[codecov]

Codecov Report

❌ Patch coverage is 70.00000% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.75%. Comparing base (2b481a7) to head (7aaa85e).

Files with missing lines	Patch %	Lines
crmsh/utils.py	66.66%	6 Missing ⚠️
crmsh/ui_cluster.py	75.00%	3 Missing ⚠️

Additional details and impacted files

Flag	Coverage Δ
integration	55.19% <70.00%> (-0.01%)	⬇️
unit	52.94% <53.33%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
crmsh/qdevice.py	98.03% <ø> (-0.01%)	⬇️
crmsh/ui_cluster.py	72.71% <75.00%> (+0.17%)	⬆️
crmsh/utils.py	67.48% <66.66%> (-0.09%)	⬇️

... and 1 file with indirect coverage changes

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