RabbitMQ: Override hostname to ensure correct IP version

Change fe83b5488d enforced usage of IPv6
in case the scenario requires IPv6, but this causes the following
failure during rabbitmq startup, because hostname is sometimes resolved
to IPv4 address in CI.

```
ERROR: epmd error for host np0033504771: badarg (unknown POSIX error)
```

This makes sure that hostname env is set according to IP address
version.

Change-Id: I4d876200f0fd8b2b84d893f243fe5615352ef11d

manifests/config.pp

@@ -49,6 +49,7 @@ class openstack_integration::config (
 
   if $ipv6 {
     $host = '::1'
+    $hostname = 'localhost6'
     $ip_version = '6'
     # Note (dmsimard): ipv6 parsing in Swift and keystone_authtoken are
     # different: https://bugs.launchpad.net/swift/+bug/1610064
@@ -57,6 +58,7 @@ class openstack_integration::config (
     $tooz_url = "redis://[${host}]:6379"
   } else {
     $host = '127.0.0.1'
+    $hostname = 'localhost'
     $ip_version = '4'
     $memcached_servers = ["${host}:11211"]
     $swift_memcached_servers = $memcached_servers

manifests/rabbitmq.pp

@@ -28,7 +28,9 @@ class openstack_integration::rabbitmq {
     ssl_cert              => $::openstack_integration::params::cert_path,
     ssl_key               => "/etc/rabbitmq/ssl/private/${facts['networking']['fqdn']}.pem",
     environment_variables => {
-      'LC_ALL' => 'en_US.UTF-8',
+      'LC_ALL'            => 'en_US.UTF-8',
+      'HOSTNAME'          => $::openstack_integration::config::hostname,
+      'RABBITMQ_NODENAME' => "rabbit@${::openstack_integration::config::hostname}"
     },
     repos_ensure          => false,
     manage_python         => false,