Build custom ostree images for package-centric testing

1. Stop using curl and unzip, as this needlessly modifies images while we already have busybox that implements wget.
2. Only install freshly build packages in LAVA for non-custom images (as e.g. ostree images don’t have a package manager)
3. Install BIN_PKG_LIST packages at build time for all custom images.
4. Build and test custom ostree images.

tests:
  image-types:
    fixedfunction: [ armhf, arm64: [uboot, rpi64], amd64 ]
    hmi:           [ armhf, arm64: [rpi64], amd64 ]
  image-deployment:
    - APT
    - OSTree
  pkg_test_cmd: wpa_cli -h
  bin_pkg_list: >
    wpasupplicant
  build-custom-image: yes

This MR depends on infrastructure/apertis-image-recipes!648 (merged).

Fixes infrastructure/apertis-issues#526 (closed).