HBASE-11858 Add InterfaceAudience for classes missing it in regionserver packages.

* RpcSchedulerFactory and PriorityFunction scoped to Coproc / Phoenix based on SimpleRpcSchedulerFactory and RpcScheduler
* RegionCoprocessorHost, RegionServerCoprocessorHost set to Coproc based on their need for the Observers that are in the book section on coprocessors
* RowProcessor and BaseRowProcessor scoped to Coproc based on RowProcessorClient
* RowTooBigException scope to Public because the book says it will be thrown by the client

Other modified classes set expressly to private.

Signed-off-by: Andrew Purtell <apurtell@apache.org>
HBASE-11891 Introduce an HBaseInterfaceAudience level to denote class names that appear in configs.

Signed-off-by: Andrew Purtell <apurtell@apache.org>