lib.ptree: add acquire_cpu worker option

defaults to true

src/lib/ptree/ptree.lua

@@ -64,6 +64,7 @@ local manager_config_spec = {
 }
 
 local worker_opt_spec = {
+   acquire_cpu = {default=true}, -- Needs dedicated CPU core?
    restart_intensity = {default=0}, -- How many restarts are permitted...
    restart_period = {default=0} -- ...within period seconds.
 }
@@ -303,6 +304,7 @@ function Manager:compute_workers_aux (worker_app_graphs, worker_opts)
    for id in pairs(worker_app_graphs) do
       local worker_opt = lib.parse(worker_opts[id] or {}, worker_opt_spec)
       local worker_aux = {
+         acquire_cpu = worker_opt.acquire_cpu,
          restart = {
             period = worker_opt.restart_period,
             intensity = worker_opt.restart_intensity,
@@ -373,7 +375,9 @@ end
 function Manager:compute_scheduling_for_worker(id, app_graph)
    local ret = {}
    for k, v in pairs(self.worker_default_scheduling) do ret[k] = v end
-   ret.cpu = self:acquire_cpu_for_worker(id, app_graph)
+   if self.workers_aux[id].acquire_cpu then
+      ret.cpu = self:acquire_cpu_for_worker(id, app_graph)
+   end
    return ret
 end