HBASE-20173 [AMv2] DisableTableProcedure concurrent to ServerCrashProcedure can deadlock

HBASE-20173 [AMv2] DisableTableProcedure concurrent to ServerCrashProcedure can deadlock

Allow that DisableTableProcedue can grab a region lock before
ServerCrashProcedure can. Cater to this cricumstance where SCP
was not unable to make progress by running the search for RIT
against the crashed server a second time, post creation of all
crashed-server assignemnts. The second run will uncover such as
the above DisableTableProcedure unassign and will interrupt its
suspend allowing both procedures to make progress.

M hbase-protocol-shaded/src/main/protobuf/MasterProcedure.proto
 Add new procedure step post-assigns that reruns the RIT finder method.

M hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/AssignmentManager.java
 Make this important log more specific as to what is going on.

M hbase-server/src/main/java/org/apache/hadoop/hbase/master/assignment/UnassignProcedure.java
 Better explanation as to what is going on.

M hbase-server/src/main/java/org/apache/hadoop/hbase/master/procedure/ServerCrashProcedure.java
 Add extra step and run handleRIT a second time after we've queued up
 all SCP assigns. Also fix a but. SCP was adding an assign of a RIT
 that was actually trying to unassign (made the deadlock more likely).