Update omnibus images

• Update to omnibus-toolchain 2.1.11
• Remove EOL platforms
  • EL6
  • Debian 8
  • Ubuntu 16.04
• Switch to using Cinc Client
• Add ark cookbook as a new dep
• Remove Dockerfile.aarch64 for Ubuntu since its now the same as Dockerfile

Signed-off-by: Lance Albertson lance@osuosl.org