Improve sshd detection/logic

[vpetersson]

Currently, simply check sshd_config to determine if a particular configuration line is present. The problem with that is that it isn't bullet proof, as the default values will vary over versions.

A better way of doing this is to instead rely on the -T option in sshd, which will spit out the current version.

For instance, here we can check for root login:

$ sudo sshd -T | grep permitroot
permitrootlogin without-password

[vpetersson]

@a-martynovich this is done, right?

[a-martynovich]

@vpetersson i think we came to an agreement that this is unreliable

[vpetersson]

Sorry, yes, you're right. At least for the time being given older distros.