Use publishing API for VLANd visualisations
When deploying a VLAN, use the publishing API to download and publish the PNG from the VLANd visualisation support for the VLAN just created, using the vlan ID in the URL:
The lava-vland protocol has the vland_hostname, this can be extended to support not only the vland admin port (3080 by default) but also the visualisation port (3081 by default).
Offer the base vlan (id 1) and the test job vlan(s).
Make it explicit in the job submission that the visualisation is to be published by requiring the test writer to specify the publishing endpoint (subject to configuration on the relevant dispatcher)
Migrated from https://projects.linaro.org/browse/LAVA-549