This PR changes the way the supervisor reads and writes files from /mnt/boot. Reads will
now use the [fatrw utility](https://github.com/balena-os/fatrw/) as a way to minimize corruption of
files in the boot partition, and thus preventing possible bricking of the device.
Since this basically changes the way a lot of configurations are read, this work was being blocked because of
the way tests were being done. While there still remain a couple of legacy tests to be migrated, this PR disables
test:legacy tests when running npm run test, as the work on refactoring those tests is in progress (see #2048) and
fatrw integration is of higher priority.
Change-type: minor
This means that configuration backend tests no longer use stubs and
(mostly) avoid internal dependencies in the tests. Instead of stubs and
mock-fs, the tests use [testfs](https://github.com/balena-io-modules/mocha-pod#working-with-the-filesystem)
which allows working with a real filesystem and ensuring everything is
re-set between tests.
This is the last change needed in order to be able to merge #1971. Here is the list of changes
- [x] Migrate splash image backend tests
- [x] Migrate extlinux backend tests
- [x] Migrate config.txt backend tests
- [x] Migrate extra-uenv config tests
- [x] Migrate odmdata config tests
- [x] Migrate config utils tests
- [x] Migrate device-config tests
Change-type: patch
