Change plaintext password authentication to pubkey authentication where possible

[ogajduse]

I got you both @jaryn and @tstrych. However, I simply do not like the implementation that is using plaintext passwords. Looking at the sshpass man page, there is a -f option that allows us to pass the path to a file containing the password instead of passing password directly. Every SatLab VM has id_rsa_hudson key installed in the authorized_keys, that means we can make use of it and use pubkey auth instead of the current solution. Is that doable for all the modules that you mentioned @tstrych?

Originally posted by @ogajduse in https://github.com/SatelliteQE/robottelo/pull/8812#r690982306

[ogajduse]

We should not use password authentication, we should use public-key authentication instead. Mainly because of security reasons.