After researching a while among the plugins available, I found that
- JClouds plugin would suit better for this specific need. However there is no support of JClouds for VMWare
vSphere Cloud Plugin from Jenkins can automate the normal operations on Vsphere (creating or deleting vms, configuring, snapshots etc), but on the top of that I would need to code the layer that analyses the Jenkins queue and fires up a vm when the demand is required
Scripted cloud plugin from Jenkins allows to run scripts to run your VMs and stop them whenever they are not needed, but they need to be created at first.
VMware ESXi/vSphere Auto-Scaling Plugin from Cloudbees do the same of above but
it is a commercial / Jenkins Pro plugin and I don't have a clear idea of what it does / how it worksLooks like option 1 would be the best for my use case, but due to lack of support I will go for option two... Unless somebody here knows a better alternative?