Replace the `SSH` class by a Python library?

[aldbr]

As explained in #7025, the _ssh_call() method does not seem to work perfectly.
There exist a few popular python libraries to perform SSH operations like Fabric (Paramiko) (https://docs.fabfile.org/en/stable/).

We could investigate the possibility of using one of them instead of relying on our SSH class to perform remote operations over SSH.

[atsareg]

At the moment the SSH class was written, as far as I remember, the Paramiko was considered but was rejected as not applicable. This was very long ago and may be the situation changed. So, this can be all reviewed. Also some use cases are probably no more relevant, e.g. using gsissh instead of ssh or tunneling to another ssh login.