Remove useless trailing '\n' in /etc/hosts file.

In HA deployment mode, we've got some trailing '\n' generated at the beginning
of each controller role nodes line in the undercloud /etc/hosts [1].

[1] - http://paste.openstack.org/show/603721/

Closes-Bug: #1674697

Change-Id: Ic38bc2a5df79dadf72025f207e91a38cc0ab0a92
Signed-off-by: Gael Chamoulaud <gchamoul@redhat.com>

overcloud.j2.yaml

@@ -398,7 +398,7 @@ resources:
         -
 {% for role in roles %}
           - list_join:
-            - "\n"
+            - ""
             - {get_attr: [{{role.name}}, hosts_entry]}
 {% endfor %}