support cosa buildextend-qemu-secex

`qemu-secex` is the artifact name used in meta.json and elsewhere
so let's support calling it that way like we do for other artifacts.

The `cmd-buildextend-secex` symlink is left in place for backwards
compatibilty.

(cherry picked from commit 85931e4)

Author: dustymabe

src/cmd-buildextend-metal

@@ -21,6 +21,11 @@ case "$(basename "$0")" in
         image_type=qemu
         image_suffix=-secex
         ;;
+    "cmd-buildextend-qemu-secex")
+        secure_execution=1
+        image_type=qemu
+        image_suffix=-secex
+        ;;
     *) fatal "called as unexpected name $0";;
 esac
 

src/cmd-buildextend-qemu-secex

@@ -0,0 +1 @@
+./cmd-buildextend-metal