Refactor VR protocol FSM and fix a bunch of it

[andrewjstone]

• Reconfiguration is now properly committed in the old epoch
• Recovery uses a u64 nonce stored on disk
• NamespaceMgr no longer determines how replicas start up
• Replica determines if it needs to be in recovery or initial state based on whether the nonce exists when it starts up
• Replicas start up in primary or backup state on initial startup instead of doing a view change immediately
• Each state now has its own state specific data
  • Shared data lives in VrCtx
• funfsm is no longer used

Also:

• Remove unused debugger files
• Remove build dependencies from stop-dev in Makefile
• Add a unit test for primary state
• Add doc explaining the VR code
  • https://github.com/vmware/haret/blob/5e33345761b83771088ae9728ce4ca82f54cb124/src/vr/README.md
• Add a disk manager
  • First use case of disk manager is reading and writing nonces for recovery purposes

[andrewjstone]

Merging, as it certainly doesn't make anything worse :)