Add (parts of) qcronsub functionality into jsub:

  - To ease transition from the toolserver, set h_vmem=1.1*virtual_free
    if h_vmem<virtual_free and virtual_free is given;
  - set -once if started as qcronsub

(merged)

Change-Id: I785f48e872b08962150484b7d6af358603e5feef