Previously, any call to 'managed-host-remote-eval' and similar would
open a new SSH session to the host. With this change, an SSH session is
opened once, cached, and then reused by all subsequent calls to
'machine-ssh-session'.
* gnu/machine/ssh.scm (<machine-ssh-configuration>): Add
'this-machine-ssh-configuration'.
[session]: Mark as thunked and change default value to an
'open-machine-ssh-session*' call.
(open-machine-ssh-session, open-machine-ssh-session*): New procedures.
(machine-ssh-session): Replace inline code by call to
'open-machine-ssh-session'.
7f20e59a13