LAVA master image scripts

Merge proposals dependent on lp://qastaging/~dpigott/lava-master-image-scripts/add-master-rootfs-size-option

  1. add-master-rootfs-size-option
  2. Dependent merge proposals

lp://qastaging/~dpigott/lava-master-image-scripts/add-master-rootfs-size-option has no merge proposals.