This commit removes and now forbids all uses of
com.google.common.collect.Maps across the codebase. This is one of many
steps in the eventual removal of Guava as a dependency.
Relates #13224
Multicast has known issues (see #12999 and #12993). This change moves
multicast into a plugin, and deprecates it in the docs. It also allows
for plugging in multiple zen ping implementations.
closes#13019