Migrate remaining hard-coded IPv4 loopback to 'localhost'

For IPv6 compatibility, use of IPv4 loopback addresses should instead
use 'localhost', which should resolve to both IPv4 and IPv6 addresses.

provider/dummy/environs.go adds both IPv4 and IPv6 loopback addresses to
the machine, rather than 'localhost', to still add scoped IP addresses
and to reflect what we expect to see in other providers.

Tests using loopback addresses have not be changed, as they should still
be correct as tests.

container/kvm/template.go

@@ -36,8 +36,8 @@ var kvmTemplate = `
     </console>
     <input type='mouse' bus='ps2'/>
     <input type='keyboard' bus='ps2'/>
-    <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'>
-      <listen type='address' address='127.0.0.1'/>
+    <graphics type='vnc' port='-1' autoport='yes' listen='localhost'>
+      <listen type='address' address='localhost'/>
     </graphics>
     <video>
       <model type='cirrus' vram='9216' heads='1'/>

juju/testing/instance.go

@@ -190,7 +190,7 @@ func fillinStartInstanceParams(env environs.Environ, machineId string, isControl
 			Config: testing.FakeControllerConfig(),
 			MongoInfo: &mongo.MongoInfo{
 				Info: mongo.Info{
-					Addrs:  []string{"127.0.0.1:1234"},
+					Addrs:  []string{"localhost:1234"},
 					CACert: "CA CERT\n" + testing.CACert,
 				},
 				Password: "mongosecret",

network/address.go

@@ -169,7 +169,7 @@ func NewAddressOnSpace(spaceName string, value string) Address {
 	return addr
 }
 
-// NewAddresses is a convenience function to create addresses from a a variable
+// NewAddresses is a convenience function to create addresses from a variable
 // number of string arguments.
 func NewAddresses(inAddresses ...string) (outAddresses []Address) {
 	outAddresses = make([]Address, len(inAddresses))

provider/dummy/environs.go

@@ -981,7 +981,9 @@ func (e *environ) StartInstance(args environs.StartInstanceParams) (*environs.St
 	series := args.Tools.OneSeries()
 
 	idString := fmt.Sprintf("%s-%d", e.name, estate.maxId)
-	addrs := network.NewAddresses(idString+".dns", "127.0.0.1")
+	// Add the addresses we want to see in the machine doc. This means both
+	// IPv4 and IPv6 loopback, as well as the DNS name.
+	addrs := network.NewAddresses(idString+".dns", "127.0.0.1", "::1")
 	logger.Debugf("StartInstance addresses: %v", addrs)
 	i := &dummyInstance{
 		id:           instance.Id(idString),