obs: Try to handle races when fetching the build log

Sometimes OBS returns an empty build log while the status of the package is building both before and after the call to osc remotebuildlog.

Try to handle that by:

1. spinning if the build.log is empty and the status is in progress
2. spinning if after the build.log has been retrieved the status is not complete yet

Case in point: https://gitlab.apertis.org/pkg/target/systemd/-/jobs/464657#L34