first cut at propagation of errors from subprocesses
bumping work limit to 512 to avoid baloon creation error
ensuring correct symlink is used for expanded disk backing
fixes partition layout in deployed partition image

When a partition image is registered, it is converted by
the imaging worker into a disk. That disk has two partitions,
listed out of order in the MBR so that sda1 is root and sda2
is the boot partition into which the worker copies the kernel
and ramdisk. When such an image is deployed on a node controller,
two more partitions are added to the disk (swap and ephemeral),
and then all four partitions are re-added to the MBR.

fixes EUCA-9251
Merge branch 'dev/dmitrii/workflow-negative-fixes' into testing