net-test: build_rootfs - fix -n being ignored

Bug: 126465735
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I8b980a5830e85cd5c4fd8d123c9911cfdf4daea7
diff --git a/net/test/build_rootfs.sh b/net/test/build_rootfs.sh
index ce09da1..07106cc 100755
--- a/net/test/build_rootfs.sh
+++ b/net/test/build_rootfs.sh
@@ -66,7 +66,9 @@
   esac
 done
 
-name=net_test.rootfs.$arch.`date +%Y%m%d`
+if [[ -z "${name}" ]]; then
+  name=net_test.rootfs.$arch.`date +%Y%m%d`
+fi
 
 # Switch to qemu-debootstrap for incompatible architectures
 if [ "$arch" = "arm64" ]; then