github: more build status normalisation
github: more build status normalisation

This continue the work done in #315 and ensure that description
are properly trim as well as truncated. This is useful to have
a consistent way to read/write build status description in
datakit.

Signed-off-by: Thomas Gazagnaire <5f50a84c1fa3bcff146405017f36aec1a10a9e38@gazagnaire.org>

docker/datakit,docker/datakit,docker/datakit