Update the file for IPv4-only or IPv6-only network

Clean the interface template file by making both IP versions independent,
including when using LXC containers.

Co-Authored-By: Yongfeng Du <dolpher.du@intel.com>

Change-Id: If0843502fe0a85cbd5eff777d9260c90cea4812a
Closes-Bug:#1355171

nova/tests/unit/network/test_network_info.py

@@ -743,6 +743,52 @@ iface eth0 inet6 static
         template = self._setup_injected_network_scenario(use_ipv4=False)
         self.assertEqual(expected, template)
 
+    def test_injection_ipv6_only(self):
+        expected = '''\
+# Injected by Nova on instance boot
+#
+# This file describes the network interfaces available on your system
+# and how to activate them. For more information, see interfaces(5).
+
+# The loopback network interface
+auto lo
+iface lo inet loopback
+
+auto eth0
+iface eth0 inet6 static
+    hwaddress ether aa:aa:aa:aa:aa:aa
+    address 1234:567::2
+    netmask 48
+    gateway 1234:567::1
+    dns-nameservers 2001:4860:4860::8888 2001:4860:4860::8844
+'''
+        template = self._setup_injected_network_scenario(use_ipv4=False,
+                                                         use_ipv6=True)
+        self.assertEqual(expected, template)
+
+    def test_injection_ipv6_only_no_gateway(self):
+        expected = '''\
+# Injected by Nova on instance boot
+#
+# This file describes the network interfaces available on your system
+# and how to activate them. For more information, see interfaces(5).
+
+# The loopback network interface
+auto lo
+iface lo inet loopback
+
+auto eth0
+iface eth0 inet6 static
+    hwaddress ether aa:aa:aa:aa:aa:aa
+    address 1234:567::2
+    netmask 48
+    dns-nameservers 2001:4860:4860::8888 2001:4860:4860::8844
+'''
+        template = self._setup_injected_network_scenario(use_ipv4=False,
+                                                         use_ipv6=True,
+                                                         gateway=False)
+        self.assertEqual(expected, template)
+
     def test_injection_ipv6_two_interfaces(self):
         expected = """\
 # Injected by Nova on instance boot

nova/virt/interfaces.template

@@ -9,6 +9,7 @@ iface lo inet loopback
 {% for ifc in interfaces %}
 
 auto {{ ifc.name }}
+{% if ifc.address %}
 iface {{ ifc.name }} inet static
     hwaddress ether {{ ifc.hwaddress }}
     address {{ ifc.address }}
@@ -20,11 +21,11 @@ iface {{ ifc.name }} inet static
 {% if ifc.dns %}
     dns-nameservers {{ ifc.dns }}
 {% endif %}
-{% if use_ipv6 %}
-{% if libvirt_virt_type == 'lxc' %}
-{% if ifc.address_v6 %}
-    post-up ip -6 addr add {{ ifc.address_v6 }}/{{ifc.netmask_v6 }} dev ${IFACE}
 {% endif %}
+{% if use_ipv6 %}
+{% if ifc.address_v6 %}
+{% if libvirt_virt_type == 'lxc' %}
+    post-up ip -6 addr add {{ ifc.address_v6 }}/{{ifc.netmask_v6 }} dev ${IFACE}
 {% if ifc.gateway_v6 %}
     post-up ip -6 route add default via {{ ifc.gateway_v6 }} dev ${IFACE}
 {% endif %}
@@ -41,4 +42,5 @@ iface {{ ifc.name }} inet6 static
 {% endif %}
 {% endif %}
 {% endif %}
+{% endif %}
 {% endfor %}