Access internal hosts via apex proxy. From the compute nodes we first
open an SSH connection to apex, and then tunnel it through the HTTP
proxy with netcat.
This way we allow reaching internal GitLab repositories without
requiring the user to have credentials in the remote host, while we can
use multiple remotes to provide redundancy.
Allow xeon machines to optionally inherit SSF configuration such as the
NFS mount point and the network configuration.
Reviewed-by: Aleix Boné <abonerib@bsc.es>
