build: test everything under samples/

Add required steps to test.sh to set up the Zephyr environment and
run all the tests under samples/

Change-Id: I066488053d5834f98eada51d33e85819d287e6fc
Signed-off-by: Yuval Peress <peress@google.com>
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/zephyr-integration/+/109250
Reviewed-by: Rob Barnes <robbarnes@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
4 files changed