HBASE-23984 [Flakey Tests] TestMasterAbortAndRSGotKilled fails in teardown (#1311)

HBASE-23984 [Flakey Tests] TestMasterAbortAndRSGotKilled fails in teardown (#1311)

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java
 Change parameter name and add javadoc to make it more clear what the
 param actually is.

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/handler/AssignRegionHandler.java
 Move postOpenDeployTasks so if it fails to talk to the Master -- which
 can happen on cluster shutdown -- then we will do cleanup of state;
 without this the RS can get stuck and won't go down.

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/handler/CloseRegionHandler.java
 Add handleException so CRH looks more like UnassignRegionHandler and
 AssignRegionHandler around exception handling. Add a bit of doc on
 why CRH.

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/handler/UnassignRegionHandler.java
 Right shift most of the body of process so can add in a finally
 that cleans up rs.getRegionsInTransitionInRS is on exception
 (otherwise outstanding entries can stop a RS going down on cluster
 shutdown)

Signed-off-by: Nick Dimiduk <ndimiduk@apache.org>
Signed-off-by: Duo Zhang <zhangduo@apache.org>