Add error when using assume role + state bucket

[#184999423] Add AssumeRole support to bbl

Author: ystros

config/downloader.go

@@ -1,6 +1,8 @@
 package config
 
 import (
+	"errors"
+
 	"github.com/cloudfoundry/bosh-bootloader/backends"
 )
 
@@ -29,6 +31,9 @@ func (d Downloader) DownloadAndPrepareState(flags GlobalFlags) error {
 			AWSSecretAccessKey: flags.AWSSecretAccessKey,
 		}
 
+		if flags.AWSAssumeRole != "" {
+			return errors.New("Assume role not supported when using an AWS state bucket")
+		}
 	case "gcp":
 		config = backends.Config{
 			Dest:                 flags.StateDir,