Update address to localhost to be consistent with other proxies

builder/amazon/common/ssh.go

@@ -29,7 +29,7 @@ func SSHHost(e ec2Describer, sshInterface string, host string) func(multistep.St
 		}
 
 		if sshInterface == "session_manager" {
-			return "127.0.0.1", nil
+			return "localhost", nil
 		}
 
 		const tries = 2

builder/amazon/common/ssh_test.go

@@ -13,7 +13,7 @@ const (
 	publicIP        = "192.168.1.1"
 	privateDNS      = "private.dns.test"
 	publicDNS       = "public.dns.test"
-	localhost       = "127.0.0.1"
+	localhost       = "localhost"
 	sshHostTemplate = "custom.host.value"
 )