tests: Make all globals readonly
Some of the globals were set as read-only variables whilst others
weren't. However, they can all be read-only.
#
# SPDX-License-Identifier: Apache-2.0
-rootfs_sh="$BATS_TEST_DIRNAME/../rootfs-builder/rootfs.sh"
-image_builder_sh="$BATS_TEST_DIRNAME/../image-builder/image_builder.sh"
-initrd_builder_sh="$BATS_TEST_DIRNAME/../initrd-builder/initrd_builder.sh"
+readonly rootfs_sh="$BATS_TEST_DIRNAME/../rootfs-builder/rootfs.sh"
+readonly image_builder_sh="$BATS_TEST_DIRNAME/../image-builder/image_builder.sh"
+readonly initrd_builder_sh="$BATS_TEST_DIRNAME/../initrd-builder/initrd_builder.sh"
readonly tmp_dir=$(mktemp -t -d osbuilder-test.XXXXXXX)
-tmp_rootfs="${tmp_dir}/rootfs-osbuilder"
+readonly tmp_rootfs="${tmp_dir}/rootfs-osbuilder"
setup()
{
