Update ghe-host-check to detect extra port 22 error

[snh]

In some situations where port 22 is blocked, ssh will return a port 22: No route to host error instead of a port 22: Connection refused error. This PR adds handling to bin/ghe-host-check for this alternative error.

[rubiojr]

@snh looks good to me but to double check, I'm trying to figure out when that'd be the case. Firewall? trying to reach a non-routable/private network? Do you know how to reproduce this one? Are you backing up or restoring a cluster or a single VM?

[snh]

The error can be a bit misleading as it doesn't necessarily mean the backup host has no route to the GHE appliance.

It is usually caused by a firewall in the path rejecting the connection with a ICMP Admin Prohibited response. The specific use case this PR solves is those where port 22 is blocked in this way but port 122 isn't. At the moment the backup fails even though the GHE appliance might be a 2.x release that only requires port 122 be accessible for backups, this change allows it to succeed.

The easiest way to reproduce is to add the following iptables rule on a Linux based backup-utils host with iptables enabled:

iptables -I OUTPUT -p tcp -d <gheapplianceip> --dport 22 -j REJECT --reject-with icmp-admin-prohibited

[rubiojr]

Thanks @snh!