Rebase remove_nexus on mutli-node

This is basically a rebase of your remove_nexus branch with all the code that's been merged into multi-node recently (namely the HA and Ceph stuff that landed today during the US workday).  This should make https://github.com/CiscoSystems/grizzly-manifests/pull/165 mergeable again.  Feel free to ignore if you're already working it out separately.