@oesteban @effigies @chrisfilo @djarecka

i would like to change nipype's container generation and testing using the following approach:

1. generate dockerfiles using neurodocker
2. check if dockerfile hash has changed or force update is set (need to determine this from PR)
3. if force update, regenerate dockerfile
4. build docker image if needed or reload minimized image
5. run all tests via neurodocker reprozip (in parallel)
6. combine all reprozip packs into a single pack
7. generate minimized docker image using reprounzip and cache this image

if this sounds good, perhaps @kaczmarj can work on implementing this.