Quota management MMP

[tardieu]

This is a follow up to #395 listing the necessary steps to make quota management generally applicable (Minimal Marketable Product):

• Add support and test support for pre-existing AppWrappers when deploying MCAD with quota management enabled.
  • define expected MCAD restart/recovery behavior.
• Add support and test support for making changes to quota trees with running and/or pending AppWrappers.
  • define expected behavior when increasing/decreasing quotas.
• Properly combine the quota and resource checks when attempting to dispatch an AppWrapper.
  • define expected preemption behavior when combining priorities and quotas.
  • quota library: enable quota reservation, commit, and rollback.
• Extend default quota logic to quota forests
  • define expected dispatch behavior with zero, or, or multiple quota trees, with and without default quota nodes, with and without non-existent trees and/or nodes.
• Update apiVersion of quota CRD (move back to alpha or beta).
• Revise specification of quota trees and nodes in AppWrapper CRD to avoid conflicting labels.
  • decide whether to use labels or extend spec.
• Expose total capacity and available capacity to users and admins.
• Update helper tools to submit AppWrappers with quotas.
• Update documentation.