Fix agent registration

[NikolayMurha]

HI.

1. I've tried to use agent:registration recipe and I have errors.
   If I use "recipe:zabbix::server" instead of "recipes:zabbix::server" zabbix_server not found.
2. After fix it I have error Exception*: NoMethodError: zabbix_host[my.node.com](zabbix::agent_registration line 75) had an error: NoMethodError: undefined method `values' for #Array:0x000000035aad68

I propose to fix it :)

[laradji]

Hi @MurgaNikolay ,

Thanks for your PR. @guilhem are you +1 for it ?

[guilhem]

I understand the problem, but we have to fix it in a different way.

recipe vs recipes is an eternal debate and I'm sure to see Yet Another PR for this in 2 weeks.

So... I don't have a solution for now (because I don't have enough time), but I can help someone to do this work.