crowbar_join.suse: Always install chef handlers

Install chef reboot handlers also if /etc/chef/client.rb is
already available.
Would it make sense to do something like:
```
for line in 'require "/var/chef/handlers/reboot_handler"' 'other line' 'last line'; do
  grep -q -e "^$line$" /etc/chef/client.rb || echo "$line" >> /etc/chef/client.rb
done
```