Revert "qemu-options.hx: Update for reboot-timeout parameter"

Revert "qemu-options.hx: Update for reboot-timeout parameter"

This reverts commit bbd9e6985ff342cbe15b9cb7eb30e842796fbbe8.

In 20a1922032 we allowed reboot-timeout=-1 again, so update the doc
accordingly.

Signed-off-by: Han Han <hhan@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191205024821.245435-1-hhan@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
(cherry picked from commit 8937a39da22e5d5689c516a2d4ce4f2bb6a378fc)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>