`RestHandler`s are highly tied to actions so registering them in the
same place makes sense.
Removes the need to for plugins to check if they are in transport client
mode before registering a RestHandler - `getRestHandlers` isn't called
at all in transport client mode.
This caused guice to throw a massive fit about the circular dependency
between NodeClient and the allocation deciders. I broke the circular
dependency by registering the actions map with the node client after
instantiation.
8db43c0107