Fix route table importing to avoid route deletion

Import route tables using inline routes in the resource data. This
is the same way resource data is structured when routes tables are
read (and created) which enables imports to line up properly with
existing resources.

Previously, if you applied a state that included the import of a
route table, all routes in the route table would be deleted. This
bug occurred because the import function
(resourceAwsRouteTableImportState()) would return a target state
including both a route table resource and separate route resources
for each route. The route table read function
(resourceAwsRouteTableRead()) returns a state with a route table
resource having inline routes. Despite being equivalent, since the
states did not match, Terraform would delete all routes in the
route table when applying the change plan.

Fixes hashicorp#5631

Update functions names to comply with convention

This commit is planned to occur after PR hashicorp#5687 which changes the
names of these functions. In order to avoid merge conflicts at that
time, this pre-emptively renames the functions.

aws/resource_aws_route_table.go

@@ -21,7 +21,18 @@ func resourceAwsRouteTable() *schema.Resource {
 		Update: resourceAwsRouteTableUpdate,
 		Delete: resourceAwsRouteTableDelete,
 		Importer: &schema.ResourceImporter{
-			State: resourceAwsRouteTableImportState,
+			State: func(d *schema.ResourceData, meta interface{}) ([]*schema.ResourceData, error) {
+				log.Printf("[INFO] Importing Route Table ID: %s", d.Id())
+
+				err := resourceAwsRouteTableRead(d, meta)
+				if err != nil {
+					return nil, err
+				}
+
+				results := make([]*schema.ResourceData, 1)
+				results[0] = d
+				return results, nil
+			},
 		},
 
 		Schema: map[string]*schema.Schema{