Robustify deployment or script to not produce broken singularity images

[yarikoptic]

Prompted by #65 . See my last comment there for more detail. If docker partition runs out of space, create_singularities doesn't detect that and produces incomplete/broken image. Could be due to a bug in elderly singularity we use there (need to upgrade smaug finally to upgrade singularity as well), or might be our script doesn't handle failed singularity execution properly.