Generate certs on all nodes for HA

With HA, HTTPS and automatic generation of self-signed certificates, all
controller nodes except for one are missing the cert files, and the api
and novncproxy services fail to start on those nodes.

This is a workaround to generate the certs on all controller nodes when HA is
enabled.

Another possible solution (to trigger the condition for generating the certs) would be to make sure the ['api' variable](https://github.com/bkutil/barclamp-nova/blob/7cc8e23b67695ea3ce05088bebec30095e6178db/chef/cookbooks/nova/recipes/config.rb#L77) is assigned based on finding the current node, i.e:

```
if apis.length > 0
   api = apis.find { |a| a.name == node.name } || apis.first
```

For this change, though, I'm not sure if picking the ```api[0]``` has some deeper meaning (as it is also used for the keystone, dns_servers, etc. below) and so, if changing this would not break other things.