lib/modules: Pass credentials irrespective of "ExecProtocol".

Child processes do not need to support the ExecProtocol in order
to utilize credentials managed by the shell.

Change-Id: I42d1ae3a883cabf5bd8b59cfbf8579db1a44eb96
diff --git a/lib/modules/shell.go b/lib/modules/shell.go
index eec1e8e..9965aae 100644
--- a/lib/modules/shell.go
+++ b/lib/modules/shell.go
@@ -277,7 +277,7 @@
 	return fd, nil
 }
 
-// NewCustomCredentials creates a new Principal for StartWithCredentials.
+// NewCustomCredentials creates a new Principal for StartWithOpts.
 // Returns nil if the shell is not managing principals.
 func (sh *Shell) NewCustomCredentials() (cred *CustomCredentials, err error) {
 	// Create child principal.
@@ -505,12 +505,10 @@
 	}
 
 	var p *os.File
-	if opts.ExecProtocol {
-		if opts.Credentials != nil {
-			p, err = opts.Credentials.File()
-			if err != nil {
-				return nil, err
-			}
+	if opts.Credentials != nil {
+		p, err = opts.Credentials.File()
+		if err != nil {
+			return nil, err
 		}
 	}