If we override the variable with '=' instead of '+=' then extra image
features set in project's local.conf (EXTRA_IMAGE_FEATURES variable) are
discarded.
Signed-off-by: Javier Viguera <javier.viguera@digi.com>
Includes development version of packages as well as empty password root
login, and package manager.
Signed-off-by: Alex Gonzalez <alex.gonzalez@digi.com>