Fixes #8289 - cloudinit from rhev/ovirt support

so this is the foreman part to handle cloud-init from rhev and as such user_data templates
it relies on the following pending PR
https://github.com/abenari/rbovirt/pull/48
and
https://github.com/fog/fog/pull/3250
i used the following user_data sample
```json
#cloud-config
hostname: <%= @host.name %>
nicname: eth0
netmask: <%= @host.subnet.mask %>
gateway: <%= @host.subnet.gateway %> 
ip: <%= @host.ip %>
dns:
 - <%= @host.subnet.dns_primary %>
domain: <%= @host.domain %>
password: <%= root_pass %> 
ssh_authorized_keys:
 - ssh-rsa XXXX federer@bumblefoot
runcmd:
 - echo superbien > /tmp/prout1
 - echo 2280 > /tmp/prout2
```






why should we handle it differently from existing user data support