cros-test: fix autotest arg backward compat

Fix bug where autotest args are being treated as a map when they are
in fact a list.

BUG=None
TEST=ran tast-generic-list with new cros-test container using old arg passing field

Change-Id: Id756175deb82e163402a759c2bba8c3ece4fce4b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/5402255
Auto-Submit: Jack Gelinas <jackgelinas@google.com>
Commit-Queue: Derek Beckett <dbeckett@chromium.org>
Tested-by: Jack Gelinas <jackgelinas@google.com>
Reviewed-by: Derek Beckett <dbeckett@chromium.org>
(cherry picked from commit e1b5d9e1a4cfc659005d9f70136e48e1f9fb9614)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/5403486
Commit-Queue: Jack Gelinas <jackgelinas@google.com>
diff --git a/src/chromiumos/test/execution/cmd/cros-test/internal/driver/tauto_driver.go b/src/chromiumos/test/execution/cmd/cros-test/internal/driver/tauto_driver.go
index b2dc76a..f157aa4 100644
--- a/src/chromiumos/test/execution/cmd/cros-test/internal/driver/tauto_driver.go
+++ b/src/chromiumos/test/execution/cmd/cros-test/internal/driver/tauto_driver.go
@@ -248,7 +248,6 @@
 }
 
 func processArgs(req *api.CrosTestRequest) (string, error) {
-	customArgs := ""
 	suites := req.GetTestSuites()
 	// In reality; we should never have an empty suite.
 	if len(suites) > 0 {
@@ -268,17 +267,13 @@
 	}
 
 	// Backwards compatibility.
-	if customArgs == "" {
-		customAutotestArgs, _, err := common.UnpackMetadata(req)
-		if err != nil {
-			return "", err
-		}
-		subCustomArgs := ""
-		for name, value := range customAutotestArgs {
-			subCustomArgs += fmt.Sprintf(" %v=%v", name, value)
-		}
-		customArgs = subCustomArgs
-
+	customAutotestArgs, _, err := common.UnpackMetadata(req)
+	if err != nil {
+		return "", err
 	}
-	return customArgs, nil
+	subCustomArgs := ""
+	for _, arg := range customAutotestArgs {
+		subCustomArgs += fmt.Sprintf(" %v=%v", arg.Flag, arg.Value)
+	}
+	return subCustomArgs, nil
 }