Improve build log display

GitLab at most collect 4 megabytes of log output to show as part of the live job view. For failed jobs generating more log, the last log lines are only available in the artifacts, and not displayed in the live job view.
The remote build log can be retrieved in 2 times, saving and displaying the logs in the live job view up to MAX_BUILDLOG_SIZE bytes, and if the logs are bigger saving them and displaying the last END_BUILDLOG_SIZE bytes of the build log at the end.

When the git commit branch use multiple /, the PROJECT can get an incorrect path for OBS.
This is fixed by replacing CI_COMMIT_REF_NAME by CI_COMMIT_REF_SLUG, which already replace everything except 0-9 and a-z replaced by -, then replace all - with :.

Signed-off-by: Frédéric Danis frederic.danis@collabora.com