offline-nodes: add a big comment and reinstate long host names so they can actually match something

# The hosts listed below are known to be down atm.

# No builds will be dispatched to those nodes, and the nodes will be marked

# as offline in the jenkins UI.

#

# The code greps for the local hostname, i.e.

# foobar-armhf-rb

# codethink-sled23-arm64

# profitbricks-build42-amd64

#

# (name coming from the basename of the workspace directory for start-agent.sh

# and from the list in reproducible_build_service.sh for reproducible_worker.sh)

#

# This means one could specify either the FQDN or the local hostname, bearing

# in mind the FQDN will always match, whereas the shorter variant may stop

# working.

#example-armhf

#codethink23

#profitbricks42

ff4a-armhf

ff64a-armhf

jtx1c-armhf

# Also see https://pad.sfconservancy.org/p/rb-build-nodes-keep

# unstable in the past, the host is up but we are vaiting for vagrantc to confirm

# it is good enough to be enabled again.

ff64a-armhf-rb.debian.net

# disk issues, down indefinitely

ff4a-armhf-rb.debian.net

jtx1c-armhf-rb.debian.net

# temporary problems

# Down here nodes are automtically added by the maintenance job when they have

# been failing their health check for too long.