'this-machine' and 'this-machine-ssh-configuration' were useless given
that there are no thunked fields.
* gnu/machine.scm (<machine>)[this-machine]: Remove.
* gnu/machine/ssh.scm (<machine-ssh-configuration>)
[this-machine-ssh-configuration]: Remove.
* gnu/machine/ssh.scm
(machine-check-file-system-availability)[check-labeled-file-system]: Use
'source-module-closure' for '(gnu build file-systems)'.
(machine-check-initrd-modules): Unquote 'file-system-label->string' instead of
'device'.
* guix/ssh.scm (remote-authorize-signing-key): New variable.
* gnu/machine/ssh.scm (deploy-managed-host): Authorize coordinator's
signing key before any invocations of 'remote-eval'.
(deploy-managed-host): Display an error if a signing key does not exist.
* doc/guix.texi (Invoking guix deploy): Remove section describing manual
signing key authorization.
(Invoking guix deploy): Add section describing the 'authorize?' field.
* gnu/machine.scm (roll-back-machine, &deploy-error, deploy-error?)
(deploy-error-should-roll-back)
(deploy-error-captured-args): New variable.
* gnu/machine/ssh.scm (roll-back-managed-host): New variable.
* guix/scripts/deploy.scm (guix-deploy): Roll-back systems when a
deployment fails.
* doc/guix.texi (Invoking guix deploy): Add section describing
prerequisites for deploying as a non-root user.
* guix/remote.scm (remote-pipe-for-gexp): New optional 'become-command'
argument.
(%remote-eval): New optional 'become-command' argument.
(remote-eval): New 'become-command' keyword argument.
* guix/ssh.scm (remote-inferior): New optional 'become-command'
argument.
(inferior-remote-eval): New optional 'become-command' argument.
(remote-authorize-signing-key): New optional 'become-command' argument.
* gnu/machine/ssh.scm (machine-become-command): New variable.
(managed-host-remote-eval): Invoke 'remote-eval' with the
'#:become-command' keyword.
(deploy-managed-host): Invoke 'remote-authorize-signing-key' with the
'#:become-command' keyword.
* gnu/machine/ssh.scm (machine-ssh-configuration): Add 'system' field.
(managed-host-remote-eval): Pass 'system' field to 'remote-eval'.
(machine-check-building-for-appropriate-system): New variable.
(check-deployment-sanity): Add call to
'machine-check-building-for-appropriate-system'.
* doc/guix.texi (Invoking guix deploy): Describe new 'system' field.
* guix/ssh.scm (remote-system): New variable.
* guix/remote.scm (remote-eval): Use result of 'remote-system' when
lowering the G-Expression.
(remote-eval): Add 'system' keyword argument.
(trampoline): Return a <program-file> rather than a <scheme-file>.
* gnu/machine.scm (machine-system): Delete variable.
(machine-operating-system): New variable.
All callers changed.
* doc/guix.texi (Invoking guix deploy): Use the
'machine-operating-system' accessor rather than 'machine-system'.
