provider/aws: Fix RDS unexpected state config

This commit adds the `resetting-master-credentials` state to the list of
allowable pending states when creating an RDS instance. The state is
returned when creating an `aws_db_instance` from a snapshot.

Fixes #4477.

builtin/providers/aws/resource_aws_db_instance.go

@@ -383,7 +383,7 @@ func resourceAwsDbInstanceCreate(d *schema.ResourceData, meta interface{}) error
 				"[INFO] Waiting for DB Instance to be available")
 
 			stateConf := &resource.StateChangeConf{
-				Pending:    []string{"creating", "backing-up", "modifying"},
+				Pending:    []string{"creating", "backing-up", "modifying", "resetting-master-credentials"},
 				Target:     "available",
 				Refresh:    resourceAwsDbInstanceStateRefreshFunc(d, meta),
 				Timeout:    40 * time.Minute,
@@ -494,7 +494,7 @@ func resourceAwsDbInstanceCreate(d *schema.ResourceData, meta interface{}) error
 		"[INFO] Waiting for DB Instance to be available")
 
 	stateConf := &resource.StateChangeConf{
-		Pending:    []string{"creating", "backing-up", "modifying"},
+		Pending:    []string{"creating", "backing-up", "modifying", "resetting-master-credentials"},
 		Target:     "available",
 		Refresh:    resourceAwsDbInstanceStateRefreshFunc(d, meta),
 		Timeout:    40 * time.Minute,