Add support to test that the root passowrd is working as expected.
- Buildtime test: Check the hash present in the generated '/etc/shadow'.
- Runtime test: Build an armv7 image and try to login with a password.
Signed-off-by: Victor Huesca <victor.huesca@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>