.gitlab-ci.yml: swap the order of build and test stages

The test stage runs one, non-cross compiled unit test job. The build
stage runs ten cross compiled build jobs. If unit tests fail all the
cross-building has gone to waste. Swap the order to detect issues
earlier.

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