For some time, OpenSSH's option 'PermitRootLogin' has deprecated the
ambiguous argument 'without-password' with 'prohibit-password'.
* doc/guix.texi (Network Services): Replace 'without-password by
'prohibit-password.
* gnu/machine/digital-ocean.scm (guix-infect): Change system
configuration to use 'prohibit-password.
* gnu/services/ssh.scm (openssh-configuration): Change comment to use
'prohibit-password.
(openssh-config-file): Add support for 'prohibit-password to
'permit-root-login'. Warn about deprecated 'without-password usage.
* gnu/tests/ganeti.scm (%ganeti-os): Replace 'without-password by
'prohibit-password.
Signed-off-by: Tobias Geerinckx-Rice <me@tobias.gr>