Padron, Omar authored Dec 20, 2018 and Gamblin, Todd committed Dec 20, 2018

 - fixed an issue where some undesirable parts of
   the spack source tree were being copied into
   the image context.

 - added a workaround for a tty ioctl warning on
   ubuntu

 - adjusted how the main images are built so that
   `RUN spack ...` works automatically for child
   images that base themselves on them.