Drop alias from state file if missing from lambda. (#10759)

* Drop alias from state file if missing from lambda.

This commit fixes an issue where if you remove a AWS Lambda, the corresponding alias for that Lambda is also deleted.

* Added missing imports.

* Removed non-local reference to constant.

builtin/providers/aws/resource_aws_lambda_alias.go

@@ -3,8 +3,10 @@ package aws
 import (
 	"fmt"
 	"log"
+	"strings"
 
 	"github.com/aws/aws-sdk-go/aws"
+	"github.com/aws/aws-sdk-go/aws/awserr"
 	"github.com/aws/aws-sdk-go/service/lambda"
 	"github.com/hashicorp/terraform/helper/schema"
 )
@@ -82,6 +84,12 @@ func resourceAwsLambdaAliasRead(d *schema.ResourceData, meta interface{}) error
 
 	aliasConfiguration, err := conn.GetAlias(params)
 	if err != nil {
+		if awsErr, ok := err.(awserr.Error); ok {
+			if awsErr.Code() == "ResourceNotFoundException" && strings.Contains(awsErr.Message(), "Cannot find alias arn") {
+				d.SetId("")
+				return nil
+			}
+		}
 		return err
 	}