provider/aws: Add arn attribute for DynamoDB tables

This commit exports the `arn` as well as the `id`, since IAM
roles require the full resource name rather than just the table
name. I'd even be in favor or having `arn` as the `id` since the
<region, tablename> pair is the uniqueness constraint, but this
will keep backwards compatibility:

http://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_CreateTable.html

builtin/providers/aws/resource_aws_dynamodb_table.go

@@ -283,6 +283,7 @@ func resourceAwsDynamoDbTableCreate(d *schema.ResourceData, meta interface{}) er
 		} else {
 			// No error, set ID and return
 			d.SetId(*output.TableDescription.TableName)
+			d.Set("arn", *output.TableDescription.TableARN)
 			return nil
 		}
 	}

website/source/docs/providers/aws/r/dynamodb_table.html.markdown

@@ -109,5 +109,6 @@ infinite loop in planning.
 
 The following attributes are exported:
 
+* `arn` - The arn of the table
 * `id` - The name of the table