Adapt zabbix_sender default path in Ceph to work for SUSE built container
images, where the `zabbix-agent` package installs `zabbix_sender` to
`/usr/sbin/zabbix_sender`.
Fixes: https://bugzilla.suse.com/show_bug.cgi?id=1186348 Signed-off-by: Patrick Seidensal <pseidensal@suse.com>