deprecate the "azure" backend name

Alert users to use the current "azurerm" naming.

backend/init/init.go

@@ -36,13 +36,14 @@ func init() {
 	// Our hardcoded backends. We don't need to acquire a lock here
 	// since init() code is serial and can't spawn goroutines.
 	backends = map[string]func() backend.Backend{
-		"atlas":   func() backend.Backend { return &backendatlas.Backend{} },
-		"local":   func() backend.Backend { return &backendlocal.Local{} },
-		"consul":  func() backend.Backend { return backendconsul.New() },
-		"inmem":   func() backend.Backend { return backendinmem.New() },
-		"swift":   func() backend.Backend { return backendSwift.New() },
-		"s3":      func() backend.Backend { return backendS3.New() },
-		"azure":   func() backend.Backend { return backendAzure.New() },
+		"atlas":  func() backend.Backend { return &backendatlas.Backend{} },
+		"local":  func() backend.Backend { return &backendlocal.Local{} },
+		"consul": func() backend.Backend { return backendconsul.New() },
+		"inmem":  func() backend.Backend { return backendinmem.New() },
+		"swift":  func() backend.Backend { return backendSwift.New() },
+		"s3":     func() backend.Backend { return backendS3.New() },
+		"azure": deprecateBackend(backendAzure.New(),
+			`Warning: "azure" name is deprecated, please use "azurerm"`),
 		"azurerm": func() backend.Backend { return backendAzure.New() },
 	}