Security update for singularity (moderate)

Singularity was updated to version 2.6.0, bringing features, bugfixes and
security fixes.

Security issues fixed:

• CVE-2018-12021: Fixed access control on systems supporting overlay file
  system (boo#1100333).

Highlights of 2.6.0:

• Allow admin to specify a non-standard location for mksquashfs binary at
  build time with ‘–with-mksquashfs’ option #1662
• ‘–nv’ option will use
  [nvidia-container-cli](<a href=“https://github.com/NVIDIA/libnvidia-container”>https://github.com/NVIDIA/libnvidia-container</a>) if
  installed #1681
• [nvliblist.conf]
  (<a href=“https://github.com/singularityware/singularity/blob/master/etc/nvliblist.c”>https://github.com/singularityware/singularity/blob/master/etc/nvliblist.c</a>
  onf) now has a section for binaries #1681
• ‘–nv’ can be made default with all action commands in singularity.conf
  #1681
• ‘–nv’ can be controlled by env vars ‘$SINGULARITY_NV’ and
  ‘$SINGULARITY_NV_OFF’ #1681
• Restore shim init process for proper signal handling and child reaping
  when container is initiated in its own PID namespace #1221
• Add ‘-i’ option to image.create to specify the inode ratio. #1759
• Bind ‘/dev/nvidia*’ into the container when the ‘–nv’ flag is used in
  conjuction with the ‘–contain’ flag #1358
• Add ‘–no-home’ option to not mount user $HOME if it is not the $CWD and
  ‘mount home = yes’ is set. #1761
• Added support for OAUTH2 Docker registries like Azure Container Registry
  #1622

Highlights of 2.5.2:

• a new build command was added to replace create + bootstrap
• default image format is squashfs, eliminating the need to specify a size
• a localimage can be used as a build base, including ext3, sandbox, and
  other squashfs images
• singularity hub can now be used as a base with the uri
• Restore docker-extract aufs whiteout handling that implements correct
  extraction of docker container layers.

Bug fixes:

• Fix 404 when using Arch Linux bootstrap #1731
• Fix environment variables clearing while starting instances #1766
• several more bug fixes, see CHANGELOG.md for details