.ostc-ci: use build-recipe instead of build-image

There are indications that upload pipe between GitLab workers and the
OSTC GitLab instance is slowing down CI, making an otherwise fast
machine idle while it waits for network traffic.

Since the images were only consumed by LAVA and for the moment, LAVA is
disabled, switch jobs using .build-image to .build-recipe. The only
difference is that now artifacts are discarded immediately after the
build.

This is a temporary workaround that can be reverted once the situation
is debugged further.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>