Lanl/mirrors

[Paul-Ferrell]

We've added a new config file at the system level - mirrors.yaml It allows you to configure regular mirrors, build caches (including public keys), and bootstrap mirrors.

• We've replaced the mirror attribute of recipe object with a mirrors attribute that works quite differently.
• The regular (which includes build caches) mirrors are just configured as a Spack mirrors.yaml
• The bootstrap mirrors are more complicated, they'll need a bootstrap.yaml and a metadata directory each.
• Keys can be given as a path (relative to the system dir) or as a base64 encoded key.
  • In either case, key will be added to the Stackinator environment and added via the Makefile
• Passing the 'cache' on the command line is still allowed
• The mirror config option may still be allowed. Still looking at it.