Add backoff when stuck in RegionTransitionProcedure, the subclass of
AssignProcedure and UnassignProcedure. Can happen when we go to
transition but the current Region state is not what we expect.
M hbase-procedure/src/main/java/org/apache/hadoop/hbase/procedure2/Procedure.java
Add doc on being able to suspend and wait on a timeout.
M hbase-protocol-shaded/src/main/protobuf/MasterProcedure.proto
Add 'attempt' counter so we can do backoff when we get stuck.
M hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignProcedure.java
M hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/UnassignProcedure.java
Add persistence of new 'attempt' counter
M hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/RegionTransitionProcedure.java
Doc data members that are persisted by subclasses given this is 'odd'.
Add a counter for 'attempts' used when 'stuck' to implement backoff.
Add suspend with timeout when 'stuck'. Add callback when timeout is
exhausted which does wakeup of this procedure.
A hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/TestUnexpectedStateException.java
Test of backoff.
5a071dbe2b