narval #2059613 Try to get "manually launched" test [validation pending]

When the cubicweb cannot see narval (different networks with a fw in between) then it would be usefull for narval to check every 5 minutes (for example) if there are any plans awaiting execution.

done in3.2.0
load left0.000
closed by#7be07bc008e8 Poll the cubicweb instances instead of waiting for pyro calls to queue plans