How to add a new buildbot worker

[montjoie]

Adding a buildbot worker is possible, but some problem need to be solved:

• How to share secret for submitting job to LAVA
• for the moment ghelper use cp to the FILESERVER, but a remote worker will need some "network copy"
• Instead of using a centralized FILESERVER, some worker could use their local one (and so still use cp)
• LAVA could boot only from accessible FILESERVER, so a private (as non publicly accessible) worker with its own FILESERVER could only use a local LAVA

So we need to settle, does we want a central FILESERVER or not.
pro-central: all logs, binary are easily accessible for external people want to see them
pro-decentralizer: easier