feat: restart the host (reboot_host)

netOrk asks a driver for reboot_host before it offers a restart, and the
Linux driver had none, so a Linux host -- and OpenMediaVault and QTS, which
inherit this driver -- could not be restarted from netOrk at all (netOrk
#637). reboot_host runs /sbin/reboot detached and two seconds late through
_run_privileged: the launcher's exit status comes back before the host goes
down, and closing the session cannot take the restart with it. A refusal
(sudo without a password) raises with what the host said.

napalm_linux/linux.py

@@ -120,6 +120,11 @@ _REFRESH = {
 }
 _YUM_SECURITY_COMMAND = "LC_ALL=C yum updateinfo list security -q 2>/dev/null"
 
+#: Restart the host two seconds later, detached from this session: the launcher's
+#: exit status comes back before the host goes down, and closing the session
+#: cannot take the restart with it.
+_REBOOT_DETACHED = "sh -c '(trap \"\" HUP; sleep 2; /sbin/reboot) </dev/null >/dev/null 2>&1 &'"
+
 #: What to do when sudo wants a password netOrk does not have.
 _SUDO_PASSWORD_HINT = (
     "sudo requires a password on this device but none is configured in netOrk. "
@@ -389,6 +394,21 @@ class LinuxDriver(KernelFactsMixin, SystemdServicesMixin, HostStatusMixin, OSDri
             return self._sudo(command, read_timeout=timeout)
         return self._send(f"sudo -n {command}", read_timeout=timeout)
 
+    def reboot_host(self) -> None:
+        """Restart the host (``HostRebootMixin``); returns once the restart is under way.
+
+        :raises RuntimeError: when the host refuses -- sudo without a password,
+            no ``reboot`` -- or its answer carried no exit status.
+        """
+        output, status = _split_status(
+            self._run_privileged(f"{_REBOOT_DETACHED}; echo {_RC_MARKER}$?", 30)
+        )
+        if status != 0:
+            reason = output or f"the reboot command exited with status {status}"
+            if "password is required" in output:
+                reason = f"{reason}\n{_SUDO_PASSWORD_HINT}"
+            raise RuntimeError(reason)
+
     def _run_host_status_command(self, command: str) -> str:
         """The transport for ``HostStatusMixin.get_host_status``: read-only, no sudo."""
         return self._send(command, read_timeout=60)